From b9b85843572bf283f48285001e276ba7e61b63f6 Mon Sep 17 00:00:00 2001
From: Pierre Schmitz <pierre@archlinux.de>
Date: Sun, 22 Feb 2009 13:37:51 +0100
Subject: updated to MediaWiki 1.14.0

---
 includes/diff/Diff.php             |  580 ++++++++++
 includes/diff/DifferenceEngine.php | 2120 ++++++++++++++++++++++++++++++++++++
 includes/diff/HTMLDiff.php         | 1005 +++++++++++++++++
 includes/diff/Nodes.php            |  439 ++++++++
 4 files changed, 4144 insertions(+)
 create mode 100644 includes/diff/Diff.php
 create mode 100644 includes/diff/DifferenceEngine.php
 create mode 100644 includes/diff/HTMLDiff.php
 create mode 100644 includes/diff/Nodes.php

(limited to 'includes/diff')

diff --git a/includes/diff/Diff.php b/includes/diff/Diff.php
new file mode 100644
index 00000000..538c2d83
--- /dev/null
+++ b/includes/diff/Diff.php
@@ -0,0 +1,580 @@
+<?php
+/* Copyright (C) 2008 Guy Van den Broeck <guy@guyvdb.eu>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
+ * or see http://www.gnu.org/
+ */
+
+/**
+ * This diff implementation is mainly lifted from the LCS algorithm of the Eclipse project which
+ * in turn is based on Myers' "An O(ND) difference algorithm and its variations"
+ * (http://citeseer.ist.psu.edu/myers86ond.html) with range compression (see Wu et al.'s
+ * "An O(NP) Sequence Comparison Algorithm").
+ *
+ * This implementation supports an upper bound on the excution time.
+ *
+ * Complexity: O((M + N)D) worst case time, O(M + N + D^2) expected time, O(M + N) space
+ *
+ * @author Guy Van den Broeck
+ * @ingroup DifferenceEngine
+ */
+class WikiDiff3 {
+
+	//Input variables
+	private $from;
+	private $to;
+	private $m;
+	private $n;
+
+	private $tooLong;
+	private $powLimit;
+
+	//State variables
+	private $maxDifferences;
+	private $lcsLengthCorrectedForHeuristic = false;
+
+	//Output variables
+	public $length;
+	public $removed;
+	public $added;
+	public $heuristicUsed;
+
+	function __construct($tooLong = 2000000, $powLimit = 1.45){
+		$this->tooLong = $tooLong;
+		$this->powLimit = $powLimit;
+	}
+
+	public function diff(/*array*/ $from, /*array*/ $to){
+		//remember initial lengths
+		$m = sizeof($from);
+		$n = count($to);
+
+		$this->heuristicUsed = false;
+
+		//output
+		$removed = $m > 0 ? array_fill(0, $m, true) : array();
+		$added = $n > 0 ? array_fill(0, $n, true) : array();
+
+		//reduce the complexity for the next step (intentionally done twice)
+		//remove common tokens at the start
+		$i = 0;
+		while($i < $m && $i < $n && $from[$i] === $to[$i]) {
+			$removed[$i] = $added[$i] = false;
+			unset($from[$i], $to[$i]);
+			++$i;
+		}
+
+		//remove common tokens at the end
+		$j = 1;
+		while($i + $j <= $m && $i + $j <= $n && $from[$m - $j] === $to[$n - $j]) {
+			$removed[$m - $j] = $added[$n - $j] = false;
+			unset($from[$m - $j], $to[$n - $j]);
+			++$j;
+		}
+
+		$this->from = $newFromIndex = $this->to = $newToIndex = array();
+
+		//remove tokens not in both sequences
+		$shared = array();
+		foreach( $from as $key ) {
+			$shared[$key] = false;
+		}
+
+		foreach($to as $index => &$el) {
+			if(array_key_exists($el, $shared)) {
+				//keep it
+				$this->to[] = $el;
+				$shared[$el] = true;
+				$newToIndex[] = $index;
+			}
+		}
+		foreach($from as $index => &$el) {
+			if($shared[$el]) {
+				//keep it
+				$this->from[] = $el;
+				$newFromIndex[] = $index;
+			}
+		}
+
+		unset($shared, $from, $to);
+
+		$this->m = count($this->from);
+		$this->n = count($this->to);
+
+		$this->removed = $this->m > 0 ? array_fill(0, $this->m, true) : array();
+		$this->added = $this->n > 0 ? array_fill(0, $this->n, true) : array();
+
+		if ($this->m == 0 || $this->n == 0) {
+			$this->length = 0;
+		} else {
+			$this->maxDifferences = ceil(($this->m + $this->n) / 2.0);
+			if ($this->m * $this->n > $this->tooLong) {
+				// limit complexity to D^POW_LIMIT for long sequences
+				$this->maxDifferences = floor(pow($this->maxDifferences, $this->powLimit - 1.0));
+				wfDebug("Limiting max number of differences to $this->maxDifferences\n");
+			}
+
+			/*
+			 * The common prefixes and suffixes are always part of some LCS, include
+			 * them now to reduce our search space
+			 */
+			$max = min($this->m, $this->n);
+			for ($forwardBound = 0; $forwardBound < $max
+					&& $this->from[$forwardBound] === $this->to[$forwardBound];
+					++$forwardBound) {
+				$this->removed[$forwardBound] = $this->added[$forwardBound] = false;
+			}
+
+			$backBoundL1 = $this->m - 1;
+			$backBoundL2 = $this->n - 1;
+
+			while ($backBoundL1 >= $forwardBound && $backBoundL2 >= $forwardBound
+					&& $this->from[$backBoundL1] === $this->to[$backBoundL2]) {
+				$this->removed[$backBoundL1--] = $this->added[$backBoundL2--] = false;
+			}
+
+			$temp = array_fill(0, $this->m + $this->n + 1, 0);
+			$V = array($temp, $temp);
+			$snake = array(0, 0, 0);
+
+			$this->length = $forwardBound + $this->m - $backBoundL1 - 1
+				+ $this->lcs_rec($forwardBound, $backBoundL1,
+				$forwardBound, $backBoundL2, $V, $snake);
+		}
+
+		$this->m = $m;
+		$this->n = $n;
+
+		$this->length += $i + $j - 1;
+
+		foreach($this->removed as $key => &$removed_elem) {
+			if(!$removed_elem) {
+				$removed[$newFromIndex[$key]] = false;
+			}
+		}
+		foreach($this->added as $key => &$added_elem) {
+			if(!$added_elem) {
+				$added[$newToIndex[$key]] = false;
+			}
+		}
+		$this->removed = $removed;
+		$this->added = $added;
+	}
+
+	function diff_range($from_lines, $to_lines) {
+		// Diff and store locally
+		$this->diff($from_lines, $to_lines);
+		unset($from_lines, $to_lines);
+
+		$ranges = array();
+		$xi = $yi = 0;
+		while ($xi < $this->m || $yi < $this->n) {
+			// Matching "snake".
+			while ($xi < $this->m && $yi < $this->n
+					&& !$this->removed[$xi]
+					&& !$this->added[$yi]) {
+				++$xi;
+				++$yi;
+			}
+			// Find deletes & adds.
+			$xstart = $xi;
+			while ($xi < $this->m && $this->removed[$xi]) {
+				++$xi;
+			}
+
+			$ystart = $yi;
+			while ($yi < $this->n && $this->added[$yi]) {
+				++$yi;
+			}
+
+			if ($xi > $xstart || $yi > $ystart) {
+				$ranges[] = new RangeDifference($xstart, $xi,
+								$ystart, $yi);
+			}
+		}
+		return $ranges;
+	}
+
+	private function lcs_rec($bottoml1, $topl1, $bottoml2, $topl2, &$V, &$snake) {
+		// check that both sequences are non-empty
+		if ($bottoml1 > $topl1 || $bottoml2 > $topl2) {
+			return 0;
+		}
+
+		$d = $this->find_middle_snake($bottoml1, $topl1, $bottoml2,
+							$topl2, $V, $snake);
+
+		// need to store these so we don't lose them when they're
+		// overwritten by the recursion
+		$len = $snake[2];
+		$startx = $snake[0];
+		$starty = $snake[1];
+
+		// the middle snake is part of the LCS, store it
+		for ($i = 0; $i < $len; ++$i) {
+			$this->removed[$startx + $i] = $this->added[$starty + $i] = false;
+		}
+
+		if ($d > 1) {
+			return $len
+			+ $this->lcs_rec($bottoml1, $startx - 1, $bottoml2,
+							$starty - 1, $V, $snake)
+			+ $this->lcs_rec($startx + $len, $topl1, $starty + $len,
+							$topl2, $V, $snake);
+		} else if ($d == 1) {
+			/*
+			 * In this case the sequences differ by exactly 1 line. We have
+			 * already saved all the lines after the difference in the for loop
+			 * above, now we need to save all the lines before the difference.
+			 */
+			$max = min($startx - $bottoml1, $starty - $bottoml2);
+			for ($i = 0; $i < $max; ++$i) {
+				$this->removed[$bottoml1 + $i] =
+					$this->added[$bottoml2 + $i] = false;
+			}
+			return $max + $len;
+		}
+		return $len;
+	}
+
+	private function find_middle_snake($bottoml1, $topl1, $bottoml2,$topl2, &$V, &$snake) {
+		$from = &$this->from;
+		$to = &$this->to;
+		$V0 = &$V[0];
+		$V1 = &$V[1];
+		$snake0 = &$snake[0];
+		$snake1 = &$snake[1];
+		$snake2 = &$snake[2];
+		$bottoml1_min_1 = $bottoml1-1;
+		$bottoml2_min_1 = $bottoml2-1;
+		$N = $topl1 - $bottoml1_min_1;
+		$M = $topl2 - $bottoml2_min_1;
+		$delta = $N - $M;
+		$maxabsx = $N+$bottoml1;
+		$maxabsy = $M+$bottoml2;
+		$limit = min($this->maxDifferences, ceil(($N + $M ) / 2));
+
+		//value_to_add_forward: a 0 or 1 that we add to the start
+		// offset to make it odd/even
+		if (($M & 1) == 1) {
+			$value_to_add_forward = 1;
+		} else {
+			$value_to_add_forward = 0;
+		}
+
+		if (($N & 1) == 1) {
+			$value_to_add_backward = 1;
+		} else {
+			$value_to_add_backward = 0;
+		}
+
+		$start_forward = -$M;
+		$end_forward = $N;
+		$start_backward = -$N;
+		$end_backward = $M;
+
+		$limit_min_1 = $limit - 1;
+		$limit_plus_1 = $limit + 1;
+
+		$V0[$limit_plus_1] = 0;
+		$V1[$limit_min_1] = $N;
+		$limit = min($this->maxDifferences, ceil(($N + $M ) / 2));
+
+		if (($delta & 1) == 1) {
+			for ($d = 0; $d <= $limit; ++$d) {
+				$start_diag = max($value_to_add_forward + $start_forward, -$d);
+				$end_diag = min($end_forward, $d);
+				$value_to_add_forward = 1 - $value_to_add_forward;
+
+				// compute forward furthest reaching paths
+				for ($k = $start_diag; $k <= $end_diag; $k += 2) {
+					if ($k == -$d || ($k < $d
+							&& $V0[$limit_min_1 + $k] < $V0[$limit_plus_1 + $k])) {
+						$x = $V0[$limit_plus_1 + $k];
+					} else {
+						$x = $V0[$limit_min_1 + $k] + 1;
+					}
+
+					$absx = $snake0 = $x + $bottoml1;
+					$absy = $snake1 = $x - $k + $bottoml2;
+
+					while ($absx < $maxabsx && $absy < $maxabsy && $from[$absx] === $to[$absy]) {
+						++$absx;
+						++$absy;
+					}
+					$x = $absx-$bottoml1;
+
+					$snake2 = $absx -$snake0;
+					$V0[$limit + $k] = $x;
+					if ($k >= $delta - $d + 1 && $k <= $delta + $d - 1
+							&& $x >= $V1[$limit + $k - $delta]) {
+						return 2 * $d - 1;
+					}
+
+					// check to see if we can cut down the diagonal range
+					if ($x >= $N && $end_forward > $k - 1) {
+						$end_forward = $k - 1;
+					} else if ($absy - $bottoml2 >= $M) {
+						$start_forward = $k + 1;
+						$value_to_add_forward = 0;
+					}
+				}
+
+				$start_diag = max($value_to_add_backward + $start_backward, -$d);
+				$end_diag = min($end_backward, $d);
+				$value_to_add_backward = 1 - $value_to_add_backward;
+
+				// compute backward furthest reaching paths
+				for ($k = $start_diag; $k <= $end_diag; $k += 2) {
+					if ($k == $d
+					|| ($k != -$d && $V1[$limit_min_1 + $k] < $V1[$limit_plus_1 + $k])) {
+						$x = $V1[$limit_min_1 + $k];
+					} else {
+						$x = $V1[$limit_plus_1 + $k] - 1;
+					}
+
+					$y = $x - $k - $delta;
+
+					$snake2 = 0;
+					while ($x > 0 && $y > 0
+					&& $from[$x +$bottoml1_min_1] === $to[$y + $bottoml2_min_1]) {
+						--$x;
+						--$y;
+						++$snake2;
+					}
+					$V1[$limit + $k] = $x;
+
+					// check to see if we can cut down our diagonal range
+					if ($x <= 0) {
+						$start_backward = $k + 1;
+						$value_to_add_backward = 0;
+					} else if ($y <= 0 && $end_backward > $k - 1) {
+						$end_backward = $k - 1;
+					}
+				}
+			}
+		} else {
+			for ($d = 0; $d <= $limit; ++$d) {
+				$start_diag = max($value_to_add_forward + $start_forward, -$d);
+				$end_diag = min($end_forward, $d);
+				$value_to_add_forward = 1 - $value_to_add_forward;
+
+				// compute forward furthest reaching paths
+				for ($k = $start_diag; $k <= $end_diag; $k += 2) {
+					if ($k == -$d
+					|| ($k < $d && $V0[$limit_min_1 + $k] < $V0[$limit_plus_1 + $k])) {
+						$x = $V0[$limit_plus_1 + $k];
+					} else {
+						$x = $V0[$limit_min_1 + $k] + 1;
+					}
+
+					$absx = $snake0 = $x + $bottoml1;
+					$absy = $snake1 = $x - $k + $bottoml2;
+
+					while ($absx < $maxabsx && $absy < $maxabsy && $from[$absx] === $to[$absy]) {
+						++$absx;
+						++$absy;
+					}
+					$x = $absx-$bottoml1;
+					$snake2 = $absx -$snake0;
+					$V0[$limit + $k] = $x;
+
+					// check to see if we can cut down the diagonal range
+					if ($x >= $N && $end_forward > $k - 1) {
+						$end_forward = $k - 1;
+					} else if ($absy-$bottoml2 >= $M) {
+						$start_forward = $k + 1;
+						$value_to_add_forward = 0;
+					}
+				}
+
+				$start_diag = max($value_to_add_backward + $start_backward, -$d);
+				$end_diag = min($end_backward, $d);
+				$value_to_add_backward = 1 - $value_to_add_backward;
+
+				// compute backward furthest reaching paths
+				for ($k = $start_diag; $k <= $end_diag; $k += 2) {
+					if ($k == $d
+					|| ($k != -$d && $V1[$limit_min_1 + $k] < $V1[$limit_plus_1 + $k])) {
+						$x = $V1[$limit_min_1 + $k];
+					} else {
+						$x = $V1[$limit_plus_1 + $k] - 1;
+					}
+
+					$y = $x - $k - $delta;
+
+					$snake2 = 0;
+					while ($x > 0 && $y > 0
+							&& $from[$x +$bottoml1_min_1] === $to[$y + $bottoml2_min_1]) {
+						--$x;
+						--$y;
+						++$snake2;
+					}
+					$V1[$limit + $k] = $x;
+
+					if ($k >= -$delta - $d && $k <= $d - $delta
+							&& $x <= $V0[$limit + $k + $delta]) {
+						$snake0 = $bottoml1 + $x;
+						$snake1 = $bottoml2 + $y;
+						return 2 * $d;
+					}
+
+					// check to see if we can cut down our diagonal range
+					if ($x <= 0) {
+						$start_backward = $k + 1;
+						$value_to_add_backward = 0;
+					} else if ($y <= 0 && $end_backward > $k - 1) {
+						$end_backward = $k - 1;
+					}
+				}
+			}
+		}
+		/*
+		 * computing the true LCS is too expensive, instead find the diagonal
+		 * with the most progress and pretend a midle snake of length 0 occurs
+		 * there.
+		 */
+
+		$most_progress = self::findMostProgress($M, $N, $limit, $V);
+
+		$snake0 = $bottoml1 + $most_progress[0];
+		$snake1 = $bottoml2 + $most_progress[1];
+		$snake2 = 0;
+		wfDebug("Computing the LCS is too expensive. Using a heuristic.\n");
+		$this->heuristicUsed = true;
+		return 5; /*
+		* HACK: since we didn't really finish the LCS computation
+		* we don't really know the length of the SES. We don't do
+		* anything with the result anyway, unless it's <=1. We know
+		* for a fact SES > 1 so 5 is as good a number as any to
+		* return here
+		*/
+	}
+
+	private static function findMostProgress($M, $N, $limit, $V) {
+		$delta = $N - $M;
+
+		if (($M & 1) == ($limit & 1)) {
+			$forward_start_diag = max(-$M, -$limit);
+		} else {
+			$forward_start_diag = max(1 - $M, -$limit);
+		}
+
+		$forward_end_diag = min($N, $limit);
+
+		if (($N & 1) == ($limit & 1)) {
+			$backward_start_diag = max(-$N, -$limit);
+		} else {
+			$backward_start_diag = max(1 - $N, -$limit);
+		}
+
+		$backward_end_diag = -min($M, $limit);
+
+		$temp = array(0, 0, 0);
+
+
+		$max_progress = array_fill(0, ceil(max($forward_end_diag - $forward_start_diag,
+				$backward_end_diag - $backward_start_diag) / 2), $temp);
+		$num_progress = 0; // the 1st entry is current, it is initialized
+		// with 0s
+
+		// first search the forward diagonals
+		for ($k = $forward_start_diag; $k <= $forward_end_diag; $k += 2) {
+			$x = $V[0][$limit + $k];
+			$y = $x - $k;
+			if ($x > $N || $y > $M) {
+				continue;
+			}
+
+			$progress = $x + $y;
+			if ($progress > $max_progress[0][2]) {
+				$num_progress = 0;
+				$max_progress[0][0] = $x;
+				$max_progress[0][1] = $y;
+				$max_progress[0][2] = $progress;
+			} else if ($progress == $max_progress[0][2]) {
+				++$num_progress;
+				$max_progress[$num_progress][0] = $x;
+				$max_progress[$num_progress][1] = $y;
+				$max_progress[$num_progress][2] = $progress;
+			}
+		}
+
+		$max_progress_forward = true; // initially the maximum
+		// progress is in the forward
+		// direction
+
+		// now search the backward diagonals
+		for ($k = $backward_start_diag; $k <= $backward_end_diag; $k += 2) {
+			$x = $V[1][$limit + $k];
+			$y = $x - $k - $delta;
+			if ($x < 0 || $y < 0) {
+				continue;
+			}
+
+			$progress = $N - $x + $M - $y;
+			if ($progress > $max_progress[0][2]) {
+				$num_progress = 0;
+				$max_progress_forward = false;
+				$max_progress[0][0] = $x;
+				$max_progress[0][1] = $y;
+				$max_progress[0][2] = $progress;
+			} else if ($progress == $max_progress[0][2] && !$max_progress_forward) {
+				++$num_progress;
+				$max_progress[$num_progress][0] = $x;
+				$max_progress[$num_progress][1] = $y;
+				$max_progress[$num_progress][2] = $progress;
+			}
+		}
+
+		// return the middle diagonal with maximal progress.
+		return $max_progress[floor($num_progress / 2)];
+	}
+
+	public function getLcsLength(){
+		if($this->heuristicUsed && !$this->lcsLengthCorrectedForHeuristic){
+			$this->lcsLengthCorrectedForHeuristic = true;
+			$this->length = $this->m-array_sum($this->added);
+		}
+		return $this->length;
+	}
+
+}
+
+/**
+ * Alternative representation of a set of changes, by the index
+ * ranges that are changed.
+ * 
+ * @ingroup DifferenceEngine
+ */
+class RangeDifference {
+
+	public $leftstart;
+	public $leftend;
+	public $leftlength;
+
+	public $rightstart;
+	public $rightend;
+	public $rightlength;
+
+	function __construct($leftstart, $leftend, $rightstart, $rightend){
+		$this->leftstart = $leftstart;
+		$this->leftend = $leftend;
+		$this->leftlength = $leftend - $leftstart;
+		$this->rightstart = $rightstart;
+		$this->rightend = $rightend;
+		$this->rightlength = $rightend - $rightstart;
+	}
+}
diff --git a/includes/diff/DifferenceEngine.php b/includes/diff/DifferenceEngine.php
new file mode 100644
index 00000000..b30ff190
--- /dev/null
+++ b/includes/diff/DifferenceEngine.php
@@ -0,0 +1,2120 @@
+<?php
+/**
+ * @defgroup DifferenceEngine DifferenceEngine
+ */
+
+/**
+ * Constant to indicate diff cache compatibility.
+ * Bump this when changing the diff formatting in a way that
+ * fixes important bugs or such to force cached diff views to
+ * clear.
+ */
+define( 'MW_DIFF_VERSION', '1.11a' );
+
+/**
+ * @todo document
+ * @ingroup DifferenceEngine
+ */
+class DifferenceEngine {
+	/**#@+
+	 * @private
+	 */
+	var $mOldid, $mNewid, $mTitle;
+	var $mOldtitle, $mNewtitle, $mPagetitle;
+	var $mOldtext, $mNewtext;
+	var $mOldPage, $mNewPage;
+	var $mRcidMarkPatrolled;
+	var $mOldRev, $mNewRev;
+	var $mRevisionsLoaded = false; // Have the revisions been loaded
+	var $mTextLoaded = 0; // How many text blobs have been loaded, 0, 1 or 2?
+	var $htmldiff;
+	/**#@-*/
+
+	/**
+	 * Constructor
+	 * @param $titleObj Title object that the diff is associated with
+	 * @param $old Integer: old ID we want to show and diff with.
+	 * @param $new String: either 'prev' or 'next'.
+	 * @param $rcid Integer: ??? FIXME (default 0)
+	 * @param $refreshCache boolean If set, refreshes the diff cache
+	 * @param $htmldiff boolean If set, output using HTMLDiff instead of raw wikicode diff
+	 */
+	function __construct( $titleObj = null, $old = 0, $new = 0, $rcid = 0, $refreshCache = false , $htmldiff = false) {
+		$this->mTitle = $titleObj;
+		wfDebug("DifferenceEngine old '$old' new '$new' rcid '$rcid'\n");
+
+		if ( 'prev' === $new ) {
+			# Show diff between revision $old and the previous one.
+			# Get previous one from DB.
+			#
+			$this->mNewid = intval($old);
+
+			$this->mOldid = $this->mTitle->getPreviousRevisionID( $this->mNewid );
+
+		} elseif ( 'next' === $new ) {
+			# Show diff between revision $old and the previous one.
+			# Get previous one from DB.
+			#
+			$this->mOldid = intval($old);
+			$this->mNewid = $this->mTitle->getNextRevisionID( $this->mOldid );
+			if ( false === $this->mNewid ) {
+				# if no result, NewId points to the newest old revision. The only newer
+				# revision is cur, which is "0".
+				$this->mNewid = 0;
+			}
+
+		} else {
+			$this->mOldid = intval($old);
+			$this->mNewid = intval($new);
+		}
+		$this->mRcidMarkPatrolled = intval($rcid);  # force it to be an integer
+		$this->mRefreshCache = $refreshCache;
+		$this->htmldiff = $htmldiff;
+	}
+
+	function getTitle() {
+		return $this->mTitle;
+	}
+
+	function showDiffPage( $diffOnly = false ) {
+		global $wgUser, $wgOut, $wgUseExternalEditor, $wgUseRCPatrol, $wgEnableHtmlDiff;
+		wfProfileIn( __METHOD__ );
+
+
+		# If external diffs are enabled both globally and for the user,
+		# we'll use the application/x-external-editor interface to call
+		# an external diff tool like kompare, kdiff3, etc.
+		if($wgUseExternalEditor && $wgUser->getOption('externaldiff')) {
+			global $wgInputEncoding,$wgServer,$wgScript,$wgLang;
+			$wgOut->disable();
+			header ( "Content-type: application/x-external-editor; charset=".$wgInputEncoding );
+			$url1=$this->mTitle->getFullURL("action=raw&oldid=".$this->mOldid);
+			$url2=$this->mTitle->getFullURL("action=raw&oldid=".$this->mNewid);
+			$special=$wgLang->getNsText(NS_SPECIAL);
+			$control=<<<CONTROL
+			[Process]
+			Type=Diff text
+			Engine=MediaWiki
+			Script={$wgServer}{$wgScript}
+			Special namespace={$special}
+
+			[File]
+			Extension=wiki
+			URL=$url1
+
+			[File 2]
+			Extension=wiki
+			URL=$url2
+CONTROL;
+			echo($control);
+			return;
+		}
+
+		$wgOut->setArticleFlag( false );
+		if ( ! $this->loadRevisionData() ) {
+			$t = $this->mTitle->getPrefixedText();
+			$d = wfMsgExt( 'missingarticle-diff', array( 'escape' ), $this->mOldid, $this->mNewid );
+			$wgOut->setPagetitle( wfMsg( 'errorpagetitle' ) );
+			$wgOut->addWikiMsg( 'missing-article', "<nowiki>$t</nowiki>", $d );
+			wfProfileOut( __METHOD__ );
+			return;
+		}
+
+		wfRunHooks( 'DiffViewHeader', array( $this, $this->mOldRev, $this->mNewRev ) );
+
+		if ( $this->mNewRev->isCurrent() ) {
+			$wgOut->setArticleFlag( true );
+		}
+
+		# mOldid is false if the difference engine is called with a "vague" query for
+		# a diff between a version V and its previous version V' AND the version V
+		# is the first version of that article. In that case, V' does not exist.
+		if ( $this->mOldid === false ) {
+			$this->showFirstRevision();
+			$this->renderNewRevision();  // should we respect $diffOnly here or not?
+			wfProfileOut( __METHOD__ );
+			return;
+		}
+
+		$wgOut->suppressQuickbar();
+
+		$oldTitle = $this->mOldPage->getPrefixedText();
+		$newTitle = $this->mNewPage->getPrefixedText();
+		if( $oldTitle == $newTitle ) {
+			$wgOut->setPageTitle( $newTitle );
+		} else {
+			$wgOut->setPageTitle( $oldTitle . ', ' . $newTitle );
+		}
+		$wgOut->setSubtitle( wfMsgExt( 'difference', array( 'parseinline' ) ) );
+		$wgOut->setRobotPolicy( 'noindex,nofollow' );
+
+		if ( !$this->mOldPage->userCanRead() || !$this->mNewPage->userCanRead() ) {
+			$wgOut->loginToUse();
+			$wgOut->output();
+			$wgOut->disable();
+			wfProfileOut( __METHOD__ );
+			return;
+		}
+
+		$sk = $wgUser->getSkin();
+
+		// Check if page is editable
+		$editable = $this->mNewRev->getTitle()->userCan( 'edit' );
+		if ( $editable && $this->mNewRev->isCurrent() && $wgUser->isAllowed( 'rollback' ) ) {
+			$rollback = '&nbsp;&nbsp;&nbsp;' . $sk->generateRollback( $this->mNewRev );
+		} else {
+			$rollback = '';
+		}
+
+		// Prepare a change patrol link, if applicable
+		if( $wgUseRCPatrol && $this->mTitle->userCan('patrol') ) {
+			// If we've been given an explicit change identifier, use it; saves time
+			if( $this->mRcidMarkPatrolled ) {
+				$rcid = $this->mRcidMarkPatrolled;
+			} else {
+				// Look for an unpatrolled change corresponding to this diff
+				$db = wfGetDB( DB_SLAVE );
+				$change = RecentChange::newFromConds(
+				array(
+				// Add redundant user,timestamp condition so we can use the existing index
+						'rc_user_text'  => $this->mNewRev->getUserText( Revision::FOR_THIS_USER ),
+						'rc_timestamp'  => $db->timestamp( $this->mNewRev->getTimestamp() ),
+						'rc_this_oldid' => $this->mNewid,
+						'rc_last_oldid' => $this->mOldid,
+						'rc_patrolled'  => 0
+				),
+				__METHOD__
+				);
+				if( $change instanceof RecentChange ) {
+					$rcid = $change->mAttribs['rc_id'];
+				} else {
+					// None found
+					$rcid = 0;
+				}
+			}
+			// Build the link
+			if( $rcid ) {
+				$patrol = ' <span class="patrollink">[' . $sk->makeKnownLinkObj(
+					$this->mTitle,
+					wfMsgHtml( 'markaspatrolleddiff' ),
+						"action=markpatrolled&rcid={$rcid}"
+					) . ']</span>';
+			} else {
+				$patrol = '';
+			}
+		} else {
+			$patrol = '';
+		}
+
+		$htmldiffarg = $this->htmlDiffArgument();
+		$prevlink = $sk->makeKnownLinkObj( $this->mTitle, wfMsgHtml( 'previousdiff' ),
+			'diff=prev&oldid='.$this->mOldid.$htmldiffarg, '', '', 'id="differences-prevlink"' );
+		if ( $this->mNewRev->isCurrent() ) {
+			$nextlink = '&nbsp;';
+		} else {
+			$nextlink = $sk->makeKnownLinkObj( $this->mTitle, wfMsgHtml( 'nextdiff' ),
+				'diff=next&oldid='.$this->mNewid.$htmldiffarg, '', '', 'id="differences-nextlink"' );
+		}
+
+		$oldminor = '';
+		$newminor = '';
+
+		if ($this->mOldRev->mMinorEdit == 1) {
+			$oldminor = Xml::span( wfMsg( 'minoreditletter' ), 'minor' ) . ' ';
+		}
+
+		if ($this->mNewRev->mMinorEdit == 1) {
+			$newminor = Xml::span( wfMsg( 'minoreditletter' ), 'minor' ) . ' ';
+		}
+
+		$rdel = ''; $ldel = '';
+		if( $wgUser->isAllowed( 'deleterevision' ) ) {
+			$revdel = SpecialPage::getTitleFor( 'Revisiondelete' );
+			if( !$this->mOldRev->userCan( Revision::DELETED_RESTRICTED ) ) {
+				// If revision was hidden from sysops
+				$ldel = wfMsgHtml( 'rev-delundel' );
+			} else {
+				$ldel = $sk->makeKnownLinkObj( $revdel,
+				wfMsgHtml( 'rev-delundel' ),
+					'target=' . urlencode( $this->mOldRev->mTitle->getPrefixedDbkey() ) .
+					'&oldid=' . urlencode( $this->mOldRev->getId() ) );
+				// Bolden oversighted content
+				if( $this->mOldRev->isDeleted( Revision::DELETED_RESTRICTED ) )
+				$ldel = "<strong>$ldel</strong>";
+			}
+			$ldel = "&nbsp;&nbsp;&nbsp;<tt>(<small>$ldel</small>)</tt> ";
+			// We don't currently handle well changing the top revision's settings
+			if( $this->mNewRev->isCurrent() ) {
+				// If revision was hidden from sysops
+				$rdel = wfMsgHtml( 'rev-delundel' );
+			} else if( !$this->mNewRev->userCan( Revision::DELETED_RESTRICTED ) ) {
+				// If revision was hidden from sysops
+				$rdel = wfMsgHtml( 'rev-delundel' );
+			} else {
+				$rdel = $sk->makeKnownLinkObj( $revdel,
+				wfMsgHtml( 'rev-delundel' ),
+					'target=' . urlencode( $this->mNewRev->mTitle->getPrefixedDbkey() ) .
+					'&oldid=' . urlencode( $this->mNewRev->getId() ) );
+				// Bolden oversighted content
+				if( $this->mNewRev->isDeleted( Revision::DELETED_RESTRICTED ) )
+				$rdel = "<strong>$rdel</strong>";
+			}
+			$rdel = "&nbsp;&nbsp;&nbsp;<tt>(<small>$rdel</small>)</tt> ";
+		}
+
+		$oldHeader = '<div id="mw-diff-otitle1"><strong>'.$this->mOldtitle.'</strong></div>' .
+			'<div id="mw-diff-otitle2">' . $sk->revUserTools( $this->mOldRev, true ) . "</div>" .
+			'<div id="mw-diff-otitle3">' . $oldminor . $sk->revComment( $this->mOldRev, !$diffOnly, true ) . $ldel . "</div>" .
+			'<div id="mw-diff-otitle4">' . $prevlink .'</div>';
+		$newHeader = '<div id="mw-diff-ntitle1"><strong>'.$this->mNewtitle.'</strong></div>' .
+			'<div id="mw-diff-ntitle2">' . $sk->revUserTools( $this->mNewRev, true ) . " $rollback</div>" .
+			'<div id="mw-diff-ntitle3">' . $newminor . $sk->revComment( $this->mNewRev, !$diffOnly, true ) . $rdel . "</div>" .
+			'<div id="mw-diff-ntitle4">' . $nextlink . $patrol . '</div>';
+
+		if( $wgEnableHtmlDiff && $this->htmldiff) {
+			$multi = $this->getMultiNotice();
+			$wgOut->addHTML('<div class="diff-switchtype">'.$sk->makeKnownLinkObj( $this->mTitle, wfMsgHtml( 'wikicodecomparison' ),
+			'diff='.$this->mNewid.'&oldid='.$this->mOldid.'&htmldiff=0', '', '', 'id="differences-switchtype"' ).'</div>');
+			$wgOut->addHTML( $this->addHeader( '', $oldHeader, $newHeader, $multi ) );
+			$this->renderHtmlDiff();
+		} else {
+			if($wgEnableHtmlDiff){
+				$wgOut->addHTML('<div class="diff-switchtype">'.$sk->makeKnownLinkObj( $this->mTitle, wfMsgHtml( 'visualcomparison' ),
+				'diff='.$this->mNewid.'&oldid='.$this->mOldid.'&htmldiff=1', '', '', 'id="differences-switchtype"' ).'</div>');
+			}
+			$this->showDiff( $oldHeader, $newHeader );
+			if( !$diffOnly ) {
+				$this->renderNewRevision();
+			}
+		}
+		wfProfileOut( __METHOD__ );
+	}
+
+	/**
+	 * Show the new revision of the page.
+	 */
+	function renderNewRevision() {
+		global $wgOut;
+		wfProfileIn( __METHOD__ );
+
+		$wgOut->addHTML( "<hr /><h2>{$this->mPagetitle}</h2>\n" );
+		#add deleted rev tag if needed
+		if( !$this->mNewRev->userCan(Revision::DELETED_TEXT) ) {
+			$wgOut->addWikiMsg( 'rev-deleted-text-permission' );
+		} else if( $this->mNewRev->isDeleted(Revision::DELETED_TEXT) ) {
+			$wgOut->addWikiMsg( 'rev-deleted-text-view' );
+		}
+
+		if( !$this->mNewRev->isCurrent() ) {
+			$oldEditSectionSetting = $wgOut->parserOptions()->setEditSection( false );
+		}
+
+		$this->loadNewText();
+		if( is_object( $this->mNewRev ) ) {
+			$wgOut->setRevisionId( $this->mNewRev->getId() );
+		}
+
+		if ($this->mTitle->isCssJsSubpage() || $this->mTitle->isCssOrJsPage()) {
+			// Stolen from Article::view --AG 2007-10-11
+
+			// Give hooks a chance to customise the output
+			if( wfRunHooks( 'ShowRawCssJs', array( $this->mNewtext, $this->mTitle, $wgOut ) ) ) {
+				// Wrap the whole lot in a <pre> and don't parse
+				$m = array();
+				preg_match( '!\.(css|js)$!u', $this->mTitle->getText(), $m );
+				$wgOut->addHTML( "<pre class=\"mw-code mw-{$m[1]}\" dir=\"ltr\">\n" );
+				$wgOut->addHTML( htmlspecialchars( $this->mNewtext ) );
+				$wgOut->addHTML( "\n</pre>\n" );
+			}
+		} else
+		$wgOut->addWikiTextTidy( $this->mNewtext );
+
+		if( !$this->mNewRev->isCurrent() ) {
+			$wgOut->parserOptions()->setEditSection( $oldEditSectionSetting );
+		}
+
+		wfProfileOut( __METHOD__ );
+	}
+
+
+	function renderHtmlDiff() {
+		global $wgOut, $wgTitle, $wgParser, $wgDebugComments;
+		wfProfileIn( __METHOD__ );
+
+		$this->showDiffStyle();
+
+		$wgOut->addHTML( '<h2>'.wfMsgHtml( 'visual-comparison' )."</h2>\n" );
+		#add deleted rev tag if needed
+		if( !$this->mNewRev->userCan(Revision::DELETED_TEXT) ) {
+			$wgOut->addWikiMsg( 'rev-deleted-text-permission' );
+		} else if( $this->mNewRev->isDeleted(Revision::DELETED_TEXT) ) {
+			$wgOut->addWikiMsg( 'rev-deleted-text-view' );
+		}
+
+		if( !$this->mNewRev->isCurrent() ) {
+			$oldEditSectionSetting = $wgOut->parserOptions()->setEditSection( false );
+		}
+
+		$this->loadText();
+
+		// Old revision
+		if( is_object( $this->mOldRev ) ) {
+			$wgOut->setRevisionId( $this->mOldRev->getId() );
+		}
+
+		$popts = $wgOut->parserOptions();
+		$oldTidy = $popts->setTidy( true );
+		$popts->setEditSection( false );
+
+		$parserOutput = $wgParser->parse( $this->mOldtext, $wgTitle, $popts, true, true, $wgOut->getRevisionId() );
+		$popts->setTidy( $oldTidy );
+
+		//only for new?
+		//$wgOut->addParserOutputNoText( $parserOutput );
+		$oldHtml = $parserOutput->getText();
+		wfRunHooks( 'OutputPageBeforeHTML', array( &$wgOut, &$oldHtml ) );
+
+		// New revision
+		if( is_object( $this->mNewRev ) ) {
+			$wgOut->setRevisionId( $this->mNewRev->getId() );
+		}
+
+		$popts = $wgOut->parserOptions();
+		$oldTidy = $popts->setTidy( true );
+
+		$parserOutput = $wgParser->parse( $this->mNewtext, $wgTitle, $popts, true, true, $wgOut->getRevisionId() );
+		$popts->setTidy( $oldTidy );
+
+		$wgOut->addParserOutputNoText( $parserOutput );
+		$newHtml = $parserOutput->getText();
+		wfRunHooks( 'OutputPageBeforeHTML', array( &$wgOut, &$newHtml ) );
+
+		unset($parserOutput, $popts);
+
+		$differ = new HTMLDiffer(new DelegatingContentHandler($wgOut));
+		$differ->htmlDiff($oldHtml, $newHtml);
+		if ( $wgDebugComments ) {
+			$wgOut->addHTML( "\n<!-- HtmlDiff Debug Output:\n" . HTMLDiffer::getDebugOutput() . " End Debug -->" );
+		}
+
+		wfProfileOut( __METHOD__ );
+	}
+
+	/**
+	 * Show the first revision of an article. Uses normal diff headers in
+	 * contrast to normal "old revision" display style.
+	 */
+	function showFirstRevision() {
+		global $wgOut, $wgUser;
+		wfProfileIn( __METHOD__ );
+
+		# Get article text from the DB
+		#
+		if ( ! $this->loadNewText() ) {
+			$t = $this->mTitle->getPrefixedText();
+			$d = wfMsgExt( 'missingarticle-diff', array( 'escape' ), $this->mOldid, $this->mNewid );
+			$wgOut->setPagetitle( wfMsg( 'errorpagetitle' ) );
+			$wgOut->addWikiMsg( 'missing-article', "<nowiki>$t</nowiki>", $d );
+			wfProfileOut( __METHOD__ );
+			return;
+		}
+		if ( $this->mNewRev->isCurrent() ) {
+			$wgOut->setArticleFlag( true );
+		}
+
+		# Check if user is allowed to look at this page. If not, bail out.
+		#
+		if ( !$this->mTitle->userCanRead() ) {
+			$wgOut->loginToUse();
+			$wgOut->output();
+			wfProfileOut( __METHOD__ );
+			throw new MWException("Permission Error: you do not have access to view this page");
+		}
+
+		# Prepare the header box
+		#
+		$sk = $wgUser->getSkin();
+
+		$nextlink = $sk->makeKnownLinkObj( $this->mTitle, wfMsgHtml( 'nextdiff' ), 'diff=next&oldid='.$this->mNewid.$this->htmlDiffArgument(), '', '', 'id="differences-nextlink"' );
+		$header = "<div class=\"firstrevisionheader\" style=\"text-align: center\"><strong>{$this->mOldtitle}</strong><br />" .
+		$sk->revUserTools( $this->mNewRev ) . "<br />" .
+		$sk->revComment( $this->mNewRev ) . "<br />" .
+		$nextlink . "</div>\n";
+
+		$wgOut->addHTML( $header );
+
+		$wgOut->setSubtitle( wfMsgExt( 'difference', array( 'parseinline' ) ) );
+		$wgOut->setRobotPolicy( 'noindex,nofollow' );
+
+		wfProfileOut( __METHOD__ );
+	}
+
+	function htmlDiffArgument(){
+		global $wgEnableHtmlDiff;
+		if($wgEnableHtmlDiff){
+			if($this->htmldiff){
+				return '&htmldiff=1';
+			}else{
+				return '&htmldiff=0';
+			}
+		}else{
+			return '';
+		}
+	}
+
+	/**
+	 * Get the diff text, send it to $wgOut
+	 * Returns false if the diff could not be generated, otherwise returns true
+	 */
+	function showDiff( $otitle, $ntitle ) {
+		global $wgOut;
+		$diff = $this->getDiff( $otitle, $ntitle );
+		if ( $diff === false ) {
+			$wgOut->addWikiMsg( 'missing-article', "<nowiki>(fixme, bug)</nowiki>", '' );
+			return false;
+		} else {
+			$this->showDiffStyle();
+			$wgOut->addHTML( $diff );
+			return true;
+		}
+	}
+
+	/**
+	 * Add style sheets and supporting JS for diff display.
+	 */
+	function showDiffStyle() {
+		global $wgStylePath, $wgStyleVersion, $wgOut;
+		$wgOut->addStyle( 'common/diff.css' );
+
+		// JS is needed to detect old versions of Mozilla to work around an annoyance bug.
+		$wgOut->addScript( "<script type=\"text/javascript\" src=\"$wgStylePath/common/diff.js?$wgStyleVersion\"></script>" );
+	}
+
+	/**
+	 * Get complete diff table, including header
+	 *
+	 * @param Title $otitle Old title
+	 * @param Title $ntitle New title
+	 * @return mixed
+	 */
+	function getDiff( $otitle, $ntitle ) {
+		$body = $this->getDiffBody();
+		if ( $body === false ) {
+			return false;
+		} else {
+			$multi = $this->getMultiNotice();
+			return $this->addHeader( $body, $otitle, $ntitle, $multi );
+		}
+	}
+
+	/**
+	 * Get the diff table body, without header
+	 *
+	 * @return mixed
+	 */
+	function getDiffBody() {
+		global $wgMemc;
+		wfProfileIn( __METHOD__ );
+		// Check if the diff should be hidden from this user
+		if ( $this->mOldRev && !$this->mOldRev->userCan(Revision::DELETED_TEXT) ) {
+			return '';
+		} else if ( $this->mNewRev && !$this->mNewRev->userCan(Revision::DELETED_TEXT) ) {
+			return '';
+		}
+		// Cacheable?
+		$key = false;
+		if ( $this->mOldid && $this->mNewid ) {
+			$key = wfMemcKey( 'diff', 'version', MW_DIFF_VERSION, 'oldid', $this->mOldid, 'newid', $this->mNewid );
+			// Try cache
+			if ( !$this->mRefreshCache ) {
+				$difftext = $wgMemc->get( $key );
+				if ( $difftext ) {
+					wfIncrStats( 'diff_cache_hit' );
+					$difftext = $this->localiseLineNumbers( $difftext );
+					$difftext .= "\n<!-- diff cache key $key -->\n";
+					wfProfileOut( __METHOD__ );
+					return $difftext;
+				}
+			} // don't try to load but save the result
+		}
+
+		// Loadtext is permission safe, this just clears out the diff
+		if ( !$this->loadText() ) {
+			wfProfileOut( __METHOD__ );
+			return false;
+		}
+
+		$difftext = $this->generateDiffBody( $this->mOldtext, $this->mNewtext );
+
+		// Save to cache for 7 days
+		if ( !wfRunHooks( 'AbortDiffCache', array( &$this ) ) ) {
+			wfIncrStats( 'diff_uncacheable' );
+		} else if ( $key !== false && $difftext !== false ) {
+			wfIncrStats( 'diff_cache_miss' );
+			$wgMemc->set( $key, $difftext, 7*86400 );
+		} else {
+			wfIncrStats( 'diff_uncacheable' );
+		}
+		// Replace line numbers with the text in the user's language
+		if ( $difftext !== false ) {
+			$difftext = $this->localiseLineNumbers( $difftext );
+		}
+		wfProfileOut( __METHOD__ );
+		return $difftext;
+	}
+
+	/**
+	 * Generate a diff, no caching
+	 * $otext and $ntext must be already segmented
+	 */
+	function generateDiffBody( $otext, $ntext ) {
+		global $wgExternalDiffEngine, $wgContLang;
+
+		$otext = str_replace( "\r\n", "\n", $otext );
+		$ntext = str_replace( "\r\n", "\n", $ntext );
+
+		if ( $wgExternalDiffEngine == 'wikidiff' ) {
+			# For historical reasons, external diff engine expects
+			# input text to be HTML-escaped already
+			$otext = htmlspecialchars ( $wgContLang->segmentForDiff( $otext ) );
+			$ntext = htmlspecialchars ( $wgContLang->segmentForDiff( $ntext ) );
+			if( !function_exists( 'wikidiff_do_diff' ) ) {
+				dl('php_wikidiff.so');
+			}
+			return $wgContLang->unsegementForDiff( wikidiff_do_diff( $otext, $ntext, 2 ) ) .
+			$this->debug( 'wikidiff1' );
+		}
+
+		if ( $wgExternalDiffEngine == 'wikidiff2' ) {
+			# Better external diff engine, the 2 may some day be dropped
+			# This one does the escaping and segmenting itself
+			if ( !function_exists( 'wikidiff2_do_diff' ) ) {
+				wfProfileIn( __METHOD__ . "-dl" );
+				@dl('php_wikidiff2.so');
+				wfProfileOut( __METHOD__ . "-dl" );
+			}
+			if ( function_exists( 'wikidiff2_do_diff' ) ) {
+				wfProfileIn( 'wikidiff2_do_diff' );
+				$text = wikidiff2_do_diff( $otext, $ntext, 2 );
+				$text .= $this->debug( 'wikidiff2' );
+				wfProfileOut( 'wikidiff2_do_diff' );
+				return $text;
+			}
+		}
+		if ( $wgExternalDiffEngine != 'wikidiff3' && $wgExternalDiffEngine !== false ) {
+			# Diff via the shell
+			global $wgTmpDirectory;
+			$tempName1 = tempnam( $wgTmpDirectory, 'diff_' );
+			$tempName2 = tempnam( $wgTmpDirectory, 'diff_' );
+
+			$tempFile1 = fopen( $tempName1, "w" );
+			if ( !$tempFile1 ) {
+				wfProfileOut( __METHOD__ );
+				return false;
+			}
+			$tempFile2 = fopen( $tempName2, "w" );
+			if ( !$tempFile2 ) {
+				wfProfileOut( __METHOD__ );
+				return false;
+			}
+			fwrite( $tempFile1, $otext );
+			fwrite( $tempFile2, $ntext );
+			fclose( $tempFile1 );
+			fclose( $tempFile2 );
+			$cmd = wfEscapeShellArg( $wgExternalDiffEngine, $tempName1, $tempName2 );
+			wfProfileIn( __METHOD__ . "-shellexec" );
+			$difftext = wfShellExec( $cmd );
+			$difftext .= $this->debug( "external $wgExternalDiffEngine" );
+			wfProfileOut( __METHOD__ . "-shellexec" );
+			unlink( $tempName1 );
+			unlink( $tempName2 );
+			return $difftext;
+		}
+
+		# Native PHP diff
+		$ota = explode( "\n", $wgContLang->segmentForDiff( $otext ) );
+		$nta = explode( "\n", $wgContLang->segmentForDiff( $ntext ) );
+		$diffs = new Diff( $ota, $nta );
+		$formatter = new TableDiffFormatter();
+		return $wgContLang->unsegmentForDiff( $formatter->format( $diffs ) ) .
+		$this->debug();
+	}
+
+	/**
+	 * Generate a debug comment indicating diff generating time,
+	 * server node, and generator backend.
+	 */
+	protected function debug( $generator="internal" ) {
+		global $wgShowHostnames;
+		$data = array( $generator );
+		if( $wgShowHostnames ) {
+			$data[] = wfHostname();
+		}
+		$data[] = wfTimestamp( TS_DB );
+		return "<!-- diff generator: " .
+		implode( " ",
+		array_map(
+					"htmlspecialchars",
+		$data ) ) .
+			" -->\n";
+	}
+
+	/**
+	 * Replace line numbers with the text in the user's language
+	 */
+	function localiseLineNumbers( $text ) {
+		return preg_replace_callback( '/<!--LINE (\d+)-->/',
+		array( &$this, 'localiseLineNumbersCb' ), $text );
+	}
+
+	function localiseLineNumbersCb( $matches ) {
+		global $wgLang;
+		return wfMsgExt( 'lineno', array( 'parseinline' ), $wgLang->formatNum( $matches[1] ) );
+	}
+
+
+	/**
+	 * If there are revisions between the ones being compared, return a note saying so.
+	 */
+	function getMultiNotice() {
+		if ( !is_object($this->mOldRev) || !is_object($this->mNewRev) )
+		return '';
+
+		if( !$this->mOldPage->equals( $this->mNewPage ) ) {
+			// Comparing two different pages? Count would be meaningless.
+			return '';
+		}
+
+		$oldid = $this->mOldRev->getId();
+		$newid = $this->mNewRev->getId();
+		if ( $oldid > $newid ) {
+			$tmp = $oldid; $oldid = $newid; $newid = $tmp;
+		}
+
+		$n = $this->mTitle->countRevisionsBetween( $oldid, $newid );
+		if ( !$n )
+		return '';
+
+		return wfMsgExt( 'diff-multi', array( 'parseinline' ), $n );
+	}
+
+
+	/**
+	 * Add the header to a diff body
+	 */
+	static function addHeader( $diff, $otitle, $ntitle, $multi = '' ) {
+		$header = "
+		<table class='diff'>
+		<col class='diff-marker' />
+		<col class='diff-content' />
+		<col class='diff-marker' />
+		<col class='diff-content' />
+		<tr valign='top'>
+		<td colspan='2' class='diff-otitle'>{$otitle}</td>
+		<td colspan='2' class='diff-ntitle'>{$ntitle}</td>
+		</tr>
+		";
+
+		if ( $multi != '' )
+		$header .= "<tr><td colspan='4' align='center' class='diff-multi'>{$multi}</td></tr>";
+
+		return $header . $diff . "</table>";
+	}
+
+	/**
+	 * Use specified text instead of loading from the database
+	 */
+	function setText( $oldText, $newText ) {
+		$this->mOldtext = $oldText;
+		$this->mNewtext = $newText;
+		$this->mTextLoaded = 2;
+	}
+
+	/**
+	 * Load revision metadata for the specified articles. If newid is 0, then compare
+	 * the old article in oldid to the current article; if oldid is 0, then
+	 * compare the current article to the immediately previous one (ignoring the
+	 * value of newid).
+	 *
+	 * If oldid is false, leave the corresponding revision object set
+	 * to false. This is impossible via ordinary user input, and is provided for
+	 * API convenience.
+	 */
+	function loadRevisionData() {
+		global $wgLang, $wgUser;
+		if ( $this->mRevisionsLoaded ) {
+			return true;
+		} else {
+			// Whether it succeeds or fails, we don't want to try again
+			$this->mRevisionsLoaded = true;
+		}
+
+		// Load the new revision object
+		$this->mNewRev = $this->mNewid
+		? Revision::newFromId( $this->mNewid )
+		: Revision::newFromTitle( $this->mTitle );
+		if( !$this->mNewRev instanceof Revision )
+		return false;
+
+		// Update the new revision ID in case it was 0 (makes life easier doing UI stuff)
+		$this->mNewid = $this->mNewRev->getId();
+
+		// Check if page is editable
+		$editable = $this->mNewRev->getTitle()->userCan( 'edit' );
+
+		// Set assorted variables
+		$timestamp = $wgLang->timeanddate( $this->mNewRev->getTimestamp(), true );
+		$this->mNewPage = $this->mNewRev->getTitle();
+		if( $this->mNewRev->isCurrent() ) {
+			$newLink = $this->mNewPage->escapeLocalUrl( 'oldid=' . $this->mNewid );
+			$this->mPagetitle = wfMsgHTML( 'currentrev-asof', $timestamp );
+			$newEdit = $this->mNewPage->escapeLocalUrl( 'action=edit' );
+
+			$this->mNewtitle = "<a href='$newLink'>{$this->mPagetitle}</a>";
+			$this->mNewtitle .= " (<a href='$newEdit'>" . wfMsgHtml( $editable ? 'editold' : 'viewsourceold' ) . "</a>)";
+
+		} else {
+			$newLink = $this->mNewPage->escapeLocalUrl( 'oldid=' . $this->mNewid );
+			$newEdit = $this->mNewPage->escapeLocalUrl( 'action=edit&oldid=' . $this->mNewid );
+			$this->mPagetitle = wfMsgHTML( 'revisionasof', $timestamp );
+
+			$this->mNewtitle = "<a href='$newLink'>{$this->mPagetitle}</a>";
+			$this->mNewtitle .= " (<a href='$newEdit'>" . wfMsgHtml( $editable ? 'editold' : 'viewsourceold' ) . "</a>)";
+		}
+		if ( !$this->mNewRev->userCan(Revision::DELETED_TEXT) ) {
+			$this->mNewtitle = "<span class='history-deleted'>{$this->mPagetitle}</span>";
+		} else if ( $this->mNewRev->isDeleted(Revision::DELETED_TEXT) ) {
+			$this->mNewtitle = '<span class="history-deleted">'.$this->mNewtitle.'</span>';
+		}
+
+		// Load the old revision object
+		$this->mOldRev = false;
+		if( $this->mOldid ) {
+			$this->mOldRev = Revision::newFromId( $this->mOldid );
+		} elseif ( $this->mOldid === 0 ) {
+			$rev = $this->mNewRev->getPrevious();
+			if( $rev ) {
+				$this->mOldid = $rev->getId();
+				$this->mOldRev = $rev;
+			} else {
+				// No previous revision; mark to show as first-version only.
+				$this->mOldid = false;
+				$this->mOldRev = false;
+			}
+		}/* elseif ( $this->mOldid === false ) leave mOldRev false; */
+
+		if( is_null( $this->mOldRev ) ) {
+			return false;
+		}
+
+		if ( $this->mOldRev ) {
+			$this->mOldPage = $this->mOldRev->getTitle();
+
+			$t = $wgLang->timeanddate( $this->mOldRev->getTimestamp(), true );
+			$oldLink = $this->mOldPage->escapeLocalUrl( 'oldid=' . $this->mOldid );
+			$oldEdit = $this->mOldPage->escapeLocalUrl( 'action=edit&oldid=' . $this->mOldid );
+			$this->mOldPagetitle = htmlspecialchars( wfMsg( 'revisionasof', $t ) );
+
+			$this->mOldtitle = "<a href='$oldLink'>{$this->mOldPagetitle}</a>"
+			. " (<a href='$oldEdit'>" . wfMsgHtml( $editable ? 'editold' : 'viewsourceold' ) . "</a>)";
+			// Add an "undo" link
+			$newUndo = $this->mNewPage->escapeLocalUrl( 'action=edit&undoafter=' . $this->mOldid . '&undo=' . $this->mNewid);
+			$htmlLink = htmlspecialchars( wfMsg( 'editundo' ) );
+			$htmlTitle = $wgUser->getSkin()->tooltip( 'undo' );
+			if( $editable && !$this->mOldRev->isDeleted( Revision::DELETED_TEXT ) && !$this->mNewRev->isDeleted( Revision::DELETED_TEXT ) ) {
+				$this->mNewtitle .= " (<a href='$newUndo' $htmlTitle>" . $htmlLink . "</a>)";
+			}
+
+			if( !$this->mOldRev->userCan( Revision::DELETED_TEXT ) ) {
+				$this->mOldtitle = '<span class="history-deleted">' . $this->mOldPagetitle . '</span>';
+			} else if( $this->mOldRev->isDeleted( Revision::DELETED_TEXT ) ) {
+				$this->mOldtitle = '<span class="history-deleted">' . $this->mOldtitle . '</span>';
+			}
+		}
+
+		return true;
+	}
+
+	/**
+	 * Load the text of the revisions, as well as revision data.
+	 */
+	function loadText() {
+		if ( $this->mTextLoaded == 2 ) {
+			return true;
+		} else {
+			// Whether it succeeds or fails, we don't want to try again
+			$this->mTextLoaded = 2;
+		}
+
+		if ( !$this->loadRevisionData() ) {
+			return false;
+		}
+		if ( $this->mOldRev ) {
+			$this->mOldtext = $this->mOldRev->getText( Revision::FOR_THIS_USER );
+			if ( $this->mOldtext === false ) {
+				return false;
+			}
+		}
+		if ( $this->mNewRev ) {
+			$this->mNewtext = $this->mNewRev->getText( Revision::FOR_THIS_USER );
+			if ( $this->mNewtext === false ) {
+				return false;
+			}
+		}
+		return true;
+	}
+
+	/**
+	 * Load the text of the new revision, not the old one
+	 */
+	function loadNewText() {
+		if ( $this->mTextLoaded >= 1 ) {
+			return true;
+		} else {
+			$this->mTextLoaded = 1;
+		}
+		if ( !$this->loadRevisionData() ) {
+			return false;
+		}
+		$this->mNewtext = $this->mNewRev->getText();
+		return true;
+	}
+
+
+}
+
+// A PHP diff engine for phpwiki. (Taken from phpwiki-1.3.3)
+//
+// Copyright (C) 2000, 2001 Geoffrey T. Dairiki <dairiki@dairiki.org>
+// You may copy this code freely under the conditions of the GPL.
+//
+
+define('USE_ASSERTS', function_exists('assert'));
+
+/**
+ * @todo document
+ * @private
+ * @ingroup DifferenceEngine
+ */
+class _DiffOp {
+	var $type;
+	var $orig;
+	var $closing;
+
+	function reverse() {
+		trigger_error('pure virtual', E_USER_ERROR);
+	}
+
+	function norig() {
+		return $this->orig ? sizeof($this->orig) : 0;
+	}
+
+	function nclosing() {
+		return $this->closing ? sizeof($this->closing) : 0;
+	}
+}
+
+/**
+ * @todo document
+ * @private
+ * @ingroup DifferenceEngine
+ */
+class _DiffOp_Copy extends _DiffOp {
+	var $type = 'copy';
+
+	function _DiffOp_Copy ($orig, $closing = false) {
+		if (!is_array($closing))
+		$closing = $orig;
+		$this->orig = $orig;
+		$this->closing = $closing;
+	}
+
+	function reverse() {
+		return new _DiffOp_Copy($this->closing, $this->orig);
+	}
+}
+
+/**
+ * @todo document
+ * @private
+ * @ingroup DifferenceEngine
+ */
+class _DiffOp_Delete extends _DiffOp {
+	var $type = 'delete';
+
+	function _DiffOp_Delete ($lines) {
+		$this->orig = $lines;
+		$this->closing = false;
+	}
+
+	function reverse() {
+		return new _DiffOp_Add($this->orig);
+	}
+}
+
+/**
+ * @todo document
+ * @private
+ * @ingroup DifferenceEngine
+ */
+class _DiffOp_Add extends _DiffOp {
+	var $type = 'add';
+
+	function _DiffOp_Add ($lines) {
+		$this->closing = $lines;
+		$this->orig = false;
+	}
+
+	function reverse() {
+		return new _DiffOp_Delete($this->closing);
+	}
+}
+
+/**
+ * @todo document
+ * @private
+ * @ingroup DifferenceEngine
+ */
+class _DiffOp_Change extends _DiffOp {
+	var $type = 'change';
+
+	function _DiffOp_Change ($orig, $closing) {
+		$this->orig = $orig;
+		$this->closing = $closing;
+	}
+
+	function reverse() {
+		return new _DiffOp_Change($this->closing, $this->orig);
+	}
+}
+
+/**
+ * Class used internally by Diff to actually compute the diffs.
+ *
+ * The algorithm used here is mostly lifted from the perl module
+ * Algorithm::Diff (version 1.06) by Ned Konz, which is available at:
+ *	 http://www.perl.com/CPAN/authors/id/N/NE/NEDKONZ/Algorithm-Diff-1.06.zip
+ *
+ * More ideas are taken from:
+ *	 http://www.ics.uci.edu/~eppstein/161/960229.html
+ *
+ * Some ideas are (and a bit of code) are from from analyze.c, from GNU
+ * diffutils-2.7, which can be found at:
+ *	 ftp://gnudist.gnu.org/pub/gnu/diffutils/diffutils-2.7.tar.gz
+ *
+ * closingly, some ideas (subdivision by NCHUNKS > 2, and some optimizations)
+ * are my own.
+ *
+ * Line length limits for robustness added by Tim Starling, 2005-08-31
+ * Alternative implementation added by Guy Van den Broeck, 2008-07-30
+ *
+ * @author Geoffrey T. Dairiki, Tim Starling, Guy Van den Broeck
+ * @private
+ * @ingroup DifferenceEngine
+ */
+class _DiffEngine {
+
+	const MAX_XREF_LENGTH =  10000;
+
+	function diff ($from_lines, $to_lines){
+		wfProfileIn( __METHOD__ );
+
+		// Diff and store locally
+		$this->diff_local($from_lines, $to_lines);
+
+		// Merge edits when possible
+		$this->_shift_boundaries($from_lines, $this->xchanged, $this->ychanged);
+		$this->_shift_boundaries($to_lines, $this->ychanged, $this->xchanged);
+
+		// Compute the edit operations.
+		$n_from = sizeof($from_lines);
+		$n_to = sizeof($to_lines);
+
+		$edits = array();
+		$xi = $yi = 0;
+		while ($xi < $n_from || $yi < $n_to) {
+			USE_ASSERTS && assert($yi < $n_to || $this->xchanged[$xi]);
+			USE_ASSERTS && assert($xi < $n_from || $this->ychanged[$yi]);
+
+			// Skip matching "snake".
+			$copy = array();
+			while ( $xi < $n_from && $yi < $n_to
+			&& !$this->xchanged[$xi] && !$this->ychanged[$yi]) {
+				$copy[] = $from_lines[$xi++];
+				++$yi;
+			}
+			if ($copy)
+			$edits[] = new _DiffOp_Copy($copy);
+
+			// Find deletes & adds.
+			$delete = array();
+			while ($xi < $n_from && $this->xchanged[$xi])
+			$delete[] = $from_lines[$xi++];
+
+			$add = array();
+			while ($yi < $n_to && $this->ychanged[$yi])
+			$add[] = $to_lines[$yi++];
+
+			if ($delete && $add)
+			$edits[] = new _DiffOp_Change($delete, $add);
+			elseif ($delete)
+			$edits[] = new _DiffOp_Delete($delete);
+			elseif ($add)
+			$edits[] = new _DiffOp_Add($add);
+		}
+		wfProfileOut( __METHOD__ );
+		return $edits;
+	}
+
+	function diff_local ($from_lines, $to_lines) {
+		global $wgExternalDiffEngine;
+		wfProfileIn( __METHOD__);
+
+		if($wgExternalDiffEngine == 'wikidiff3'){
+			// wikidiff3
+			$wikidiff3 = new WikiDiff3();
+			$wikidiff3->diff($from_lines, $to_lines);
+			$this->xchanged = $wikidiff3->removed;
+			$this->ychanged = $wikidiff3->added;
+			unset($wikidiff3);
+		}else{
+			// old diff
+			$n_from = sizeof($from_lines);
+			$n_to = sizeof($to_lines);
+			$this->xchanged = $this->ychanged = array();
+			$this->xv = $this->yv = array();
+			$this->xind = $this->yind = array();
+			unset($this->seq);
+			unset($this->in_seq);
+			unset($this->lcs);
+
+			// Skip leading common lines.
+			for ($skip = 0; $skip < $n_from && $skip < $n_to; $skip++) {
+				if ($from_lines[$skip] !== $to_lines[$skip])
+				break;
+				$this->xchanged[$skip] = $this->ychanged[$skip] = false;
+			}
+			// Skip trailing common lines.
+			$xi = $n_from; $yi = $n_to;
+			for ($endskip = 0; --$xi > $skip && --$yi > $skip; $endskip++) {
+				if ($from_lines[$xi] !== $to_lines[$yi])
+				break;
+				$this->xchanged[$xi] = $this->ychanged[$yi] = false;
+			}
+
+			// Ignore lines which do not exist in both files.
+			for ($xi = $skip; $xi < $n_from - $endskip; $xi++) {
+				$xhash[$this->_line_hash($from_lines[$xi])] = 1;
+			}
+
+			for ($yi = $skip; $yi < $n_to - $endskip; $yi++) {
+				$line = $to_lines[$yi];
+				if ( ($this->ychanged[$yi] = empty($xhash[$this->_line_hash($line)])) )
+				continue;
+				$yhash[$this->_line_hash($line)] = 1;
+				$this->yv[] = $line;
+				$this->yind[] = $yi;
+			}
+			for ($xi = $skip; $xi < $n_from - $endskip; $xi++) {
+				$line = $from_lines[$xi];
+				if ( ($this->xchanged[$xi] = empty($yhash[$this->_line_hash($line)])) )
+				continue;
+				$this->xv[] = $line;
+				$this->xind[] = $xi;
+			}
+
+			// Find the LCS.
+			$this->_compareseq(0, sizeof($this->xv), 0, sizeof($this->yv));
+		}
+		wfProfileOut( __METHOD__ );
+	}
+
+	/**
+	 * Returns the whole line if it's small enough, or the MD5 hash otherwise
+	 */
+	function _line_hash( $line ) {
+		if ( strlen( $line ) > self::MAX_XREF_LENGTH ) {
+			return md5( $line );
+		} else {
+			return $line;
+		}
+	}
+
+	/* Divide the Largest Common Subsequence (LCS) of the sequences
+	 * [XOFF, XLIM) and [YOFF, YLIM) into NCHUNKS approximately equally
+	 * sized segments.
+	 *
+	 * Returns (LCS, PTS).	LCS is the length of the LCS. PTS is an
+	 * array of NCHUNKS+1 (X, Y) indexes giving the diving points between
+	 * sub sequences.  The first sub-sequence is contained in [X0, X1),
+	 * [Y0, Y1), the second in [X1, X2), [Y1, Y2) and so on.  Note
+	 * that (X0, Y0) == (XOFF, YOFF) and
+	 * (X[NCHUNKS], Y[NCHUNKS]) == (XLIM, YLIM).
+	 *
+	 * This function assumes that the first lines of the specified portions
+	 * of the two files do not match, and likewise that the last lines do not
+	 * match.  The caller must trim matching lines from the beginning and end
+	 * of the portions it is going to specify.
+	 */
+	function _diag ($xoff, $xlim, $yoff, $ylim, $nchunks) {
+		$flip = false;
+
+		if ($xlim - $xoff > $ylim - $yoff) {
+			// Things seems faster (I'm not sure I understand why)
+			// when the shortest sequence in X.
+			$flip = true;
+			list ($xoff, $xlim, $yoff, $ylim)
+			= array( $yoff, $ylim, $xoff, $xlim);
+		}
+
+		if ($flip)
+		for ($i = $ylim - 1; $i >= $yoff; $i--)
+		$ymatches[$this->xv[$i]][] = $i;
+		else
+		for ($i = $ylim - 1; $i >= $yoff; $i--)
+		$ymatches[$this->yv[$i]][] = $i;
+
+		$this->lcs = 0;
+		$this->seq[0]= $yoff - 1;
+		$this->in_seq = array();
+		$ymids[0] = array();
+
+		$numer = $xlim - $xoff + $nchunks - 1;
+		$x = $xoff;
+		for ($chunk = 0; $chunk < $nchunks; $chunk++) {
+			if ($chunk > 0)
+			for ($i = 0; $i <= $this->lcs; $i++)
+			$ymids[$i][$chunk-1] = $this->seq[$i];
+
+			$x1 = $xoff + (int)(($numer + ($xlim-$xoff)*$chunk) / $nchunks);
+			for ( ; $x < $x1; $x++) {
+				$line = $flip ? $this->yv[$x] : $this->xv[$x];
+				if (empty($ymatches[$line]))
+				continue;
+				$matches = $ymatches[$line];
+				reset($matches);
+				while (list ($junk, $y) = each($matches))
+				if (empty($this->in_seq[$y])) {
+					$k = $this->_lcs_pos($y);
+					USE_ASSERTS && assert($k > 0);
+					$ymids[$k] = $ymids[$k-1];
+					break;
+				}
+				while (list ( /* $junk */, $y) = each($matches)) {
+					if ($y > $this->seq[$k-1]) {
+						USE_ASSERTS && assert($y < $this->seq[$k]);
+						// Optimization: this is a common case:
+						//	next match is just replacing previous match.
+						$this->in_seq[$this->seq[$k]] = false;
+						$this->seq[$k] = $y;
+						$this->in_seq[$y] = 1;
+					} else if (empty($this->in_seq[$y])) {
+						$k = $this->_lcs_pos($y);
+						USE_ASSERTS && assert($k > 0);
+						$ymids[$k] = $ymids[$k-1];
+					}
+				}
+			}
+		}
+
+		$seps[] = $flip ? array($yoff, $xoff) : array($xoff, $yoff);
+		$ymid = $ymids[$this->lcs];
+		for ($n = 0; $n < $nchunks - 1; $n++) {
+			$x1 = $xoff + (int)(($numer + ($xlim - $xoff) * $n) / $nchunks);
+			$y1 = $ymid[$n] + 1;
+			$seps[] = $flip ? array($y1, $x1) : array($x1, $y1);
+		}
+		$seps[] = $flip ? array($ylim, $xlim) : array($xlim, $ylim);
+
+		return array($this->lcs, $seps);
+	}
+
+	function _lcs_pos ($ypos) {
+		$end = $this->lcs;
+		if ($end == 0 || $ypos > $this->seq[$end]) {
+			$this->seq[++$this->lcs] = $ypos;
+			$this->in_seq[$ypos] = 1;
+			return $this->lcs;
+		}
+
+		$beg = 1;
+		while ($beg < $end) {
+			$mid = (int)(($beg + $end) / 2);
+			if ( $ypos > $this->seq[$mid] )
+			$beg = $mid + 1;
+			else
+			$end = $mid;
+		}
+
+		USE_ASSERTS && assert($ypos != $this->seq[$end]);
+
+		$this->in_seq[$this->seq[$end]] = false;
+		$this->seq[$end] = $ypos;
+		$this->in_seq[$ypos] = 1;
+		return $end;
+	}
+
+	/* Find LCS of two sequences.
+	 *
+	 * The results are recorded in the vectors $this->{x,y}changed[], by
+	 * storing a 1 in the element for each line that is an insertion
+	 * or deletion (ie. is not in the LCS).
+	 *
+	 * The subsequence of file 0 is [XOFF, XLIM) and likewise for file 1.
+	 *
+	 * Note that XLIM, YLIM are exclusive bounds.
+	 * All line numbers are origin-0 and discarded lines are not counted.
+	 */
+	function _compareseq ($xoff, $xlim, $yoff, $ylim) {
+		// Slide down the bottom initial diagonal.
+		while ($xoff < $xlim && $yoff < $ylim
+		&& $this->xv[$xoff] == $this->yv[$yoff]) {
+			++$xoff;
+			++$yoff;
+		}
+
+		// Slide up the top initial diagonal.
+		while ($xlim > $xoff && $ylim > $yoff
+		&& $this->xv[$xlim - 1] == $this->yv[$ylim - 1]) {
+			--$xlim;
+			--$ylim;
+		}
+
+		if ($xoff == $xlim || $yoff == $ylim)
+		$lcs = 0;
+		else {
+			// This is ad hoc but seems to work well.
+			//$nchunks = sqrt(min($xlim - $xoff, $ylim - $yoff) / 2.5);
+			//$nchunks = max(2,min(8,(int)$nchunks));
+			$nchunks = min(7, $xlim - $xoff, $ylim - $yoff) + 1;
+			list ($lcs, $seps)
+			= $this->_diag($xoff,$xlim,$yoff, $ylim,$nchunks);
+		}
+
+		if ($lcs == 0) {
+			// X and Y sequences have no common subsequence:
+			// mark all changed.
+			while ($yoff < $ylim)
+			$this->ychanged[$this->yind[$yoff++]] = 1;
+			while ($xoff < $xlim)
+			$this->xchanged[$this->xind[$xoff++]] = 1;
+		} else {
+			// Use the partitions to split this problem into subproblems.
+			reset($seps);
+			$pt1 = $seps[0];
+			while ($pt2 = next($seps)) {
+				$this->_compareseq ($pt1[0], $pt2[0], $pt1[1], $pt2[1]);
+				$pt1 = $pt2;
+			}
+		}
+	}
+
+	/* Adjust inserts/deletes of identical lines to join changes
+	 * as much as possible.
+	 *
+	 * We do something when a run of changed lines include a
+	 * line at one end and has an excluded, identical line at the other.
+	 * We are free to choose which identical line is included.
+	 * `compareseq' usually chooses the one at the beginning,
+	 * but usually it is cleaner to consider the following identical line
+	 * to be the "change".
+	 *
+	 * This is extracted verbatim from analyze.c (GNU diffutils-2.7).
+	 */
+	function _shift_boundaries ($lines, &$changed, $other_changed) {
+		wfProfileIn( __METHOD__ );
+		$i = 0;
+		$j = 0;
+
+		USE_ASSERTS && assert('sizeof($lines) == sizeof($changed)');
+		$len = sizeof($lines);
+		$other_len = sizeof($other_changed);
+
+		while (1) {
+			/*
+			 * Scan forwards to find beginning of another run of changes.
+			 * Also keep track of the corresponding point in the other file.
+			 *
+			 * Throughout this code, $i and $j are adjusted together so that
+			 * the first $i elements of $changed and the first $j elements
+			 * of $other_changed both contain the same number of zeros
+			 * (unchanged lines).
+			 * Furthermore, $j is always kept so that $j == $other_len or
+			 * $other_changed[$j] == false.
+			 */
+			while ($j < $other_len && $other_changed[$j])
+			$j++;
+
+			while ($i < $len && ! $changed[$i]) {
+				USE_ASSERTS && assert('$j < $other_len && ! $other_changed[$j]');
+				$i++; $j++;
+				while ($j < $other_len && $other_changed[$j])
+				$j++;
+			}
+
+			if ($i == $len)
+			break;
+
+			$start = $i;
+
+			// Find the end of this run of changes.
+			while (++$i < $len && $changed[$i])
+			continue;
+
+			do {
+				/*
+				 * Record the length of this run of changes, so that
+				 * we can later determine whether the run has grown.
+				 */
+				$runlength = $i - $start;
+
+				/*
+				 * Move the changed region back, so long as the
+				 * previous unchanged line matches the last changed one.
+				 * This merges with previous changed regions.
+				 */
+				while ($start > 0 && $lines[$start - 1] == $lines[$i - 1]) {
+					$changed[--$start] = 1;
+					$changed[--$i] = false;
+					while ($start > 0 && $changed[$start - 1])
+					$start--;
+					USE_ASSERTS && assert('$j > 0');
+					while ($other_changed[--$j])
+					continue;
+					USE_ASSERTS && assert('$j >= 0 && !$other_changed[$j]');
+				}
+
+				/*
+				 * Set CORRESPONDING to the end of the changed run, at the last
+				 * point where it corresponds to a changed run in the other file.
+				 * CORRESPONDING == LEN means no such point has been found.
+				 */
+				$corresponding = $j < $other_len ? $i : $len;
+
+				/*
+				 * Move the changed region forward, so long as the
+				 * first changed line matches the following unchanged one.
+				 * This merges with following changed regions.
+				 * Do this second, so that if there are no merges,
+				 * the changed region is moved forward as far as possible.
+				 */
+				while ($i < $len && $lines[$start] == $lines[$i]) {
+					$changed[$start++] = false;
+					$changed[$i++] = 1;
+					while ($i < $len && $changed[$i])
+					$i++;
+
+					USE_ASSERTS && assert('$j < $other_len && ! $other_changed[$j]');
+					$j++;
+					if ($j < $other_len && $other_changed[$j]) {
+						$corresponding = $i;
+						while ($j < $other_len && $other_changed[$j])
+						$j++;
+					}
+				}
+			} while ($runlength != $i - $start);
+
+			/*
+			 * If possible, move the fully-merged run of changes
+			 * back to a corresponding run in the other file.
+			 */
+			while ($corresponding < $i) {
+				$changed[--$start] = 1;
+				$changed[--$i] = 0;
+				USE_ASSERTS && assert('$j > 0');
+				while ($other_changed[--$j])
+				continue;
+				USE_ASSERTS && assert('$j >= 0 && !$other_changed[$j]');
+			}
+		}
+		wfProfileOut( __METHOD__ );
+	}
+}
+
+/**
+ * Class representing a 'diff' between two sequences of strings.
+ * @todo document
+ * @private
+ * @ingroup DifferenceEngine
+ */
+class Diff
+{
+	var $edits;
+
+	/**
+	 * Constructor.
+	 * Computes diff between sequences of strings.
+	 *
+	 * @param $from_lines array An array of strings.
+	 *		  (Typically these are lines from a file.)
+	 * @param $to_lines array An array of strings.
+	 */
+	function Diff($from_lines, $to_lines) {
+		$eng = new _DiffEngine;
+		$this->edits = $eng->diff($from_lines, $to_lines);
+		//$this->_check($from_lines, $to_lines);
+	}
+
+	/**
+	 * Compute reversed Diff.
+	 *
+	 * SYNOPSIS:
+	 *
+	 *	$diff = new Diff($lines1, $lines2);
+	 *	$rev = $diff->reverse();
+	 * @return object A Diff object representing the inverse of the
+	 *				  original diff.
+	 */
+	function reverse () {
+		$rev = $this;
+		$rev->edits = array();
+		foreach ($this->edits as $edit) {
+			$rev->edits[] = $edit->reverse();
+		}
+		return $rev;
+	}
+
+	/**
+	 * Check for empty diff.
+	 *
+	 * @return bool True iff two sequences were identical.
+	 */
+	function isEmpty () {
+		foreach ($this->edits as $edit) {
+			if ($edit->type != 'copy')
+			return false;
+		}
+		return true;
+	}
+
+	/**
+	 * Compute the length of the Longest Common Subsequence (LCS).
+	 *
+	 * This is mostly for diagnostic purposed.
+	 *
+	 * @return int The length of the LCS.
+	 */
+	function lcs () {
+		$lcs = 0;
+		foreach ($this->edits as $edit) {
+			if ($edit->type == 'copy')
+			$lcs += sizeof($edit->orig);
+		}
+		return $lcs;
+	}
+
+	/**
+	 * Get the original set of lines.
+	 *
+	 * This reconstructs the $from_lines parameter passed to the
+	 * constructor.
+	 *
+	 * @return array The original sequence of strings.
+	 */
+	function orig() {
+		$lines = array();
+
+		foreach ($this->edits as $edit) {
+			if ($edit->orig)
+			array_splice($lines, sizeof($lines), 0, $edit->orig);
+		}
+		return $lines;
+	}
+
+	/**
+	 * Get the closing set of lines.
+	 *
+	 * This reconstructs the $to_lines parameter passed to the
+	 * constructor.
+	 *
+	 * @return array The sequence of strings.
+	 */
+	function closing() {
+		$lines = array();
+
+		foreach ($this->edits as $edit) {
+			if ($edit->closing)
+			array_splice($lines, sizeof($lines), 0, $edit->closing);
+		}
+		return $lines;
+	}
+
+	/**
+	 * Check a Diff for validity.
+	 *
+	 * This is here only for debugging purposes.
+	 */
+	function _check ($from_lines, $to_lines) {
+		wfProfileIn( __METHOD__ );
+		if (serialize($from_lines) != serialize($this->orig()))
+		trigger_error("Reconstructed original doesn't match", E_USER_ERROR);
+		if (serialize($to_lines) != serialize($this->closing()))
+		trigger_error("Reconstructed closing doesn't match", E_USER_ERROR);
+
+		$rev = $this->reverse();
+		if (serialize($to_lines) != serialize($rev->orig()))
+		trigger_error("Reversed original doesn't match", E_USER_ERROR);
+		if (serialize($from_lines) != serialize($rev->closing()))
+		trigger_error("Reversed closing doesn't match", E_USER_ERROR);
+
+
+		$prevtype = 'none';
+		foreach ($this->edits as $edit) {
+			if ( $prevtype == $edit->type )
+			trigger_error("Edit sequence is non-optimal", E_USER_ERROR);
+			$prevtype = $edit->type;
+		}
+
+		$lcs = $this->lcs();
+		trigger_error('Diff okay: LCS = '.$lcs, E_USER_NOTICE);
+		wfProfileOut( __METHOD__ );
+	}
+}
+
+/**
+ * @todo document, bad name.
+ * @private
+ * @ingroup DifferenceEngine
+ */
+class MappedDiff extends Diff
+{
+	/**
+	 * Constructor.
+	 *
+	 * Computes diff between sequences of strings.
+	 *
+	 * This can be used to compute things like
+	 * case-insensitve diffs, or diffs which ignore
+	 * changes in white-space.
+	 *
+	 * @param $from_lines array An array of strings.
+	 *	(Typically these are lines from a file.)
+	 *
+	 * @param $to_lines array An array of strings.
+	 *
+	 * @param $mapped_from_lines array This array should
+	 *	have the same size number of elements as $from_lines.
+	 *	The elements in $mapped_from_lines and
+	 *	$mapped_to_lines are what is actually compared
+	 *	when computing the diff.
+	 *
+	 * @param $mapped_to_lines array This array should
+	 *	have the same number of elements as $to_lines.
+	 */
+	function MappedDiff($from_lines, $to_lines,
+	$mapped_from_lines, $mapped_to_lines) {
+		wfProfileIn( __METHOD__ );
+
+		assert(sizeof($from_lines) == sizeof($mapped_from_lines));
+		assert(sizeof($to_lines) == sizeof($mapped_to_lines));
+
+		$this->Diff($mapped_from_lines, $mapped_to_lines);
+
+		$xi = $yi = 0;
+		for ($i = 0; $i < sizeof($this->edits); $i++) {
+			$orig = &$this->edits[$i]->orig;
+			if (is_array($orig)) {
+				$orig = array_slice($from_lines, $xi, sizeof($orig));
+				$xi += sizeof($orig);
+			}
+
+			$closing = &$this->edits[$i]->closing;
+			if (is_array($closing)) {
+				$closing = array_slice($to_lines, $yi, sizeof($closing));
+				$yi += sizeof($closing);
+			}
+		}
+		wfProfileOut( __METHOD__ );
+	}
+}
+
+/**
+ * A class to format Diffs
+ *
+ * This class formats the diff in classic diff format.
+ * It is intended that this class be customized via inheritance,
+ * to obtain fancier outputs.
+ * @todo document
+ * @private
+ * @ingroup DifferenceEngine
+ */
+class DiffFormatter {
+	/**
+	 * Number of leading context "lines" to preserve.
+	 *
+	 * This should be left at zero for this class, but subclasses
+	 * may want to set this to other values.
+	 */
+	var $leading_context_lines = 0;
+
+	/**
+	 * Number of trailing context "lines" to preserve.
+	 *
+	 * This should be left at zero for this class, but subclasses
+	 * may want to set this to other values.
+	 */
+	var $trailing_context_lines = 0;
+
+	/**
+	 * Format a diff.
+	 *
+	 * @param $diff object A Diff object.
+	 * @return string The formatted output.
+	 */
+	function format($diff) {
+		wfProfileIn( __METHOD__ );
+
+		$xi = $yi = 1;
+		$block = false;
+		$context = array();
+
+		$nlead = $this->leading_context_lines;
+		$ntrail = $this->trailing_context_lines;
+
+		$this->_start_diff();
+
+		foreach ($diff->edits as $edit) {
+			if ($edit->type == 'copy') {
+				if (is_array($block)) {
+					if (sizeof($edit->orig) <= $nlead + $ntrail) {
+						$block[] = $edit;
+					}
+					else{
+						if ($ntrail) {
+							$context = array_slice($edit->orig, 0, $ntrail);
+							$block[] = new _DiffOp_Copy($context);
+						}
+						$this->_block($x0, $ntrail + $xi - $x0,
+						$y0, $ntrail + $yi - $y0,
+						$block);
+						$block = false;
+					}
+				}
+				$context = $edit->orig;
+			}
+			else {
+				if (! is_array($block)) {
+					$context = array_slice($context, sizeof($context) - $nlead);
+					$x0 = $xi - sizeof($context);
+					$y0 = $yi - sizeof($context);
+					$block = array();
+					if ($context)
+					$block[] = new _DiffOp_Copy($context);
+				}
+				$block[] = $edit;
+			}
+
+			if ($edit->orig)
+			$xi += sizeof($edit->orig);
+			if ($edit->closing)
+			$yi += sizeof($edit->closing);
+		}
+
+		if (is_array($block))
+		$this->_block($x0, $xi - $x0,
+		$y0, $yi - $y0,
+		$block);
+
+		$end = $this->_end_diff();
+		wfProfileOut( __METHOD__ );
+		return $end;
+	}
+
+	function _block($xbeg, $xlen, $ybeg, $ylen, &$edits) {
+		wfProfileIn( __METHOD__ );
+		$this->_start_block($this->_block_header($xbeg, $xlen, $ybeg, $ylen));
+		foreach ($edits as $edit) {
+			if ($edit->type == 'copy')
+			$this->_context($edit->orig);
+			elseif ($edit->type == 'add')
+			$this->_added($edit->closing);
+			elseif ($edit->type == 'delete')
+			$this->_deleted($edit->orig);
+			elseif ($edit->type == 'change')
+			$this->_changed($edit->orig, $edit->closing);
+			else
+			trigger_error('Unknown edit type', E_USER_ERROR);
+		}
+		$this->_end_block();
+		wfProfileOut( __METHOD__ );
+	}
+
+	function _start_diff() {
+		ob_start();
+	}
+
+	function _end_diff() {
+		$val = ob_get_contents();
+		ob_end_clean();
+		return $val;
+	}
+
+	function _block_header($xbeg, $xlen, $ybeg, $ylen) {
+		if ($xlen > 1)
+		$xbeg .= "," . ($xbeg + $xlen - 1);
+		if ($ylen > 1)
+		$ybeg .= "," . ($ybeg + $ylen - 1);
+
+		return $xbeg . ($xlen ? ($ylen ? 'c' : 'd') : 'a') . $ybeg;
+	}
+
+	function _start_block($header) {
+		echo $header . "\n";
+	}
+
+	function _end_block() {
+	}
+
+	function _lines($lines, $prefix = ' ') {
+		foreach ($lines as $line)
+		echo "$prefix $line\n";
+	}
+
+	function _context($lines) {
+		$this->_lines($lines);
+	}
+
+	function _added($lines) {
+		$this->_lines($lines, '>');
+	}
+	function _deleted($lines) {
+		$this->_lines($lines, '<');
+	}
+
+	function _changed($orig, $closing) {
+		$this->_deleted($orig);
+		echo "---\n";
+		$this->_added($closing);
+	}
+}
+
+/**
+ * A formatter that outputs unified diffs
+ * @ingroup DifferenceEngine
+ */
+
+class UnifiedDiffFormatter extends DiffFormatter {
+	var $leading_context_lines = 2;
+	var $trailing_context_lines = 2;
+
+	function _added($lines) {
+		$this->_lines($lines, '+');
+	}
+	function _deleted($lines) {
+		$this->_lines($lines, '-');
+	}
+	function _changed($orig, $closing) {
+		$this->_deleted($orig);
+		$this->_added($closing);
+	}
+	function _block_header($xbeg, $xlen, $ybeg, $ylen) {
+		return "@@ -$xbeg,$xlen +$ybeg,$ylen @@";
+	}
+}
+
+/**
+ * A pseudo-formatter that just passes along the Diff::$edits array
+ * @ingroup DifferenceEngine
+ */
+class ArrayDiffFormatter extends DiffFormatter {
+	function format($diff) {
+		$oldline = 1;
+		$newline = 1;
+		$retval = array();
+		foreach($diff->edits as $edit)
+		switch($edit->type) {
+			case 'add':
+				foreach($edit->closing as $l) {
+					$retval[] = array(
+							'action' => 'add',
+							'new'=> $l,
+							'newline' => $newline++
+					);
+				}
+				break;
+			case 'delete':
+				foreach($edit->orig as $l) {
+					$retval[] = array(
+							'action' => 'delete',
+							'old' => $l,
+							'oldline' => $oldline++,
+					);
+				}
+				break;
+			case 'change':
+				foreach($edit->orig as $i => $l) {
+					$retval[] = array(
+							'action' => 'change',
+							'old' => $l,
+							'new' => @$edit->closing[$i],
+							'oldline' => $oldline++,
+							'newline' => $newline++,
+					);
+				}
+				break;
+			case 'copy':
+				$oldline += count($edit->orig);
+				$newline += count($edit->orig);
+		}
+		return $retval;
+	}
+}
+
+/**
+ *	Additions by Axel Boldt follow, partly taken from diff.php, phpwiki-1.3.3
+ *
+ */
+
+define('NBSP', '&#160;'); // iso-8859-x non-breaking space.
+
+/**
+ * @todo document
+ * @private
+ * @ingroup DifferenceEngine
+ */
+class _HWLDF_WordAccumulator {
+	function _HWLDF_WordAccumulator () {
+		$this->_lines = array();
+		$this->_line = '';
+		$this->_group = '';
+		$this->_tag = '';
+	}
+
+	function _flushGroup ($new_tag) {
+		if ($this->_group !== '') {
+			if ($this->_tag == 'ins')
+			$this->_line .= '<ins class="diffchange diffchange-inline">' .
+			htmlspecialchars ( $this->_group ) . '</ins>';
+			elseif ($this->_tag == 'del')
+			$this->_line .= '<del class="diffchange diffchange-inline">' .
+			htmlspecialchars ( $this->_group ) . '</del>';
+			else
+			$this->_line .= htmlspecialchars ( $this->_group );
+		}
+		$this->_group = '';
+		$this->_tag = $new_tag;
+	}
+
+	function _flushLine ($new_tag) {
+		$this->_flushGroup($new_tag);
+		if ($this->_line != '')
+		array_push ( $this->_lines, $this->_line );
+		else
+		# make empty lines visible by inserting an NBSP
+		array_push ( $this->_lines, NBSP );
+		$this->_line = '';
+	}
+
+	function addWords ($words, $tag = '') {
+		if ($tag != $this->_tag)
+		$this->_flushGroup($tag);
+
+		foreach ($words as $word) {
+			// new-line should only come as first char of word.
+			if ($word == '')
+			continue;
+			if ($word[0] == "\n") {
+				$this->_flushLine($tag);
+				$word = substr($word, 1);
+			}
+			assert(!strstr($word, "\n"));
+			$this->_group .= $word;
+		}
+	}
+
+	function getLines() {
+		$this->_flushLine('~done');
+		return $this->_lines;
+	}
+}
+
+/**
+ * @todo document
+ * @private
+ * @ingroup DifferenceEngine
+ */
+class WordLevelDiff extends MappedDiff {
+	const MAX_LINE_LENGTH = 10000;
+
+	function WordLevelDiff ($orig_lines, $closing_lines) {
+		wfProfileIn( __METHOD__ );
+
+		list ($orig_words, $orig_stripped) = $this->_split($orig_lines);
+		list ($closing_words, $closing_stripped) = $this->_split($closing_lines);
+
+		$this->MappedDiff($orig_words, $closing_words,
+		$orig_stripped, $closing_stripped);
+		wfProfileOut( __METHOD__ );
+	}
+
+	function _split($lines) {
+		wfProfileIn( __METHOD__ );
+
+		$words = array();
+		$stripped = array();
+		$first = true;
+		foreach ( $lines as $line ) {
+			# If the line is too long, just pretend the entire line is one big word
+			# This prevents resource exhaustion problems
+			if ( $first ) {
+				$first = false;
+			} else {
+				$words[] = "\n";
+				$stripped[] = "\n";
+			}
+			if ( strlen( $line ) > self::MAX_LINE_LENGTH ) {
+				$words[] = $line;
+				$stripped[] = $line;
+			} else {
+				$m = array();
+				if (preg_match_all('/ ( [^\S\n]+ | [0-9_A-Za-z\x80-\xff]+ | . ) (?: (?!< \n) [^\S\n])? /xs',
+				$line, $m))
+				{
+					$words = array_merge( $words, $m[0] );
+					$stripped = array_merge( $stripped, $m[1] );
+				}
+			}
+		}
+		wfProfileOut( __METHOD__ );
+		return array($words, $stripped);
+	}
+
+	function orig () {
+		wfProfileIn( __METHOD__ );
+		$orig = new _HWLDF_WordAccumulator;
+
+		foreach ($this->edits as $edit) {
+			if ($edit->type == 'copy')
+			$orig->addWords($edit->orig);
+			elseif ($edit->orig)
+			$orig->addWords($edit->orig, 'del');
+		}
+		$lines = $orig->getLines();
+		wfProfileOut( __METHOD__ );
+		return $lines;
+	}
+
+	function closing () {
+		wfProfileIn( __METHOD__ );
+		$closing = new _HWLDF_WordAccumulator;
+
+		foreach ($this->edits as $edit) {
+			if ($edit->type == 'copy')
+			$closing->addWords($edit->closing);
+			elseif ($edit->closing)
+			$closing->addWords($edit->closing, 'ins');
+		}
+		$lines = $closing->getLines();
+		wfProfileOut( __METHOD__ );
+		return $lines;
+	}
+}
+
+/**
+ * Wikipedia Table style diff formatter.
+ * @todo document
+ * @private
+ * @ingroup DifferenceEngine
+ */
+class TableDiffFormatter extends DiffFormatter {
+	function TableDiffFormatter() {
+		$this->leading_context_lines = 2;
+		$this->trailing_context_lines = 2;
+	}
+
+	public static function escapeWhiteSpace( $msg ) {
+		$msg = preg_replace( '/^ /m', '&nbsp; ', $msg );
+		$msg = preg_replace( '/ $/m', ' &nbsp;', $msg );
+		$msg = preg_replace( '/  /', '&nbsp; ', $msg );
+		return $msg;
+	}
+
+	function _block_header( $xbeg, $xlen, $ybeg, $ylen ) {
+		$r = '<tr><td colspan="2" class="diff-lineno"><!--LINE '.$xbeg."--></td>\n" .
+		  '<td colspan="2" class="diff-lineno"><!--LINE '.$ybeg."--></td></tr>\n";
+		return $r;
+	}
+
+	function _start_block( $header ) {
+		echo $header;
+	}
+
+	function _end_block() {
+	}
+
+	function _lines( $lines, $prefix=' ', $color='white' ) {
+	}
+
+	# HTML-escape parameter before calling this
+	function addedLine( $line ) {
+		return $this->wrapLine( '+', 'diff-addedline', $line );
+	}
+
+	# HTML-escape parameter before calling this
+	function deletedLine( $line ) {
+		return $this->wrapLine( '-', 'diff-deletedline', $line );
+	}
+
+	# HTML-escape parameter before calling this
+	function contextLine( $line ) {
+		return $this->wrapLine( ' ', 'diff-context', $line );
+	}
+
+	private function wrapLine( $marker, $class, $line ) {
+		if( $line !== '' ) {
+			// The <div> wrapper is needed for 'overflow: auto' style to scroll properly
+			$line = Xml::tags( 'div', null, $this->escapeWhiteSpace( $line ) );
+		}
+		return "<td class='diff-marker'>$marker</td><td class='$class'>$line</td>";
+	}
+
+	function emptyLine() {
+		return '<td colspan="2">&nbsp;</td>';
+	}
+
+	function _added( $lines ) {
+		foreach ($lines as $line) {
+			echo '<tr>' . $this->emptyLine() .
+			$this->addedLine( '<ins class="diffchange">' .
+			htmlspecialchars ( $line ) . '</ins>' ) . "</tr>\n";
+		}
+	}
+
+	function _deleted($lines) {
+		foreach ($lines as $line) {
+			echo '<tr>' . $this->deletedLine( '<del class="diffchange">' .
+			htmlspecialchars ( $line ) . '</del>' ) .
+			$this->emptyLine() . "</tr>\n";
+		}
+	}
+
+	function _context( $lines ) {
+		foreach ($lines as $line) {
+			echo '<tr>' .
+			$this->contextLine( htmlspecialchars ( $line ) ) .
+			$this->contextLine( htmlspecialchars ( $line ) ) . "</tr>\n";
+		}
+	}
+
+	function _changed( $orig, $closing ) {
+		wfProfileIn( __METHOD__ );
+
+		$diff = new WordLevelDiff( $orig, $closing );
+		$del = $diff->orig();
+		$add = $diff->closing();
+
+		# Notice that WordLevelDiff returns HTML-escaped output.
+		# Hence, we will be calling addedLine/deletedLine without HTML-escaping.
+
+		while ( $line = array_shift( $del ) ) {
+			$aline = array_shift( $add );
+			echo '<tr>' . $this->deletedLine( $line ) .
+			$this->addedLine( $aline ) . "</tr>\n";
+		}
+		foreach ($add as $line) {	# If any leftovers
+			echo '<tr>' . $this->emptyLine() .
+			$this->addedLine( $line ) . "</tr>\n";
+		}
+		wfProfileOut( __METHOD__ );
+	}
+}
diff --git a/includes/diff/HTMLDiff.php b/includes/diff/HTMLDiff.php
new file mode 100644
index 00000000..0698059f
--- /dev/null
+++ b/includes/diff/HTMLDiff.php
@@ -0,0 +1,1005 @@
+<?php
+
+/** Copyright (C) 2008 Guy Van den Broeck <guy@guyvdb.eu>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
+ * or see http://www.gnu.org/
+ * 
+ * @ingroup DifferenceEngine
+ */
+
+/**
+ * When detecting the last common parent of two nodes, all results are stored as
+ * a LastCommonParentResult.
+ */
+class LastCommonParentResult {
+
+	// Parent
+	public $parent;
+
+	// Splitting
+	public $splittingNeeded = false;
+
+	// Depth
+	public $lastCommonParentDepth = -1;
+
+	// Index
+	public $indexInLastCommonParent = -1;
+}
+
+class Modification{
+
+	const NONE = 1;
+	const REMOVED = 2;
+	const ADDED = 4;
+	const CHANGED = 8;
+
+	public $type;
+
+	public $id = -1;
+
+	public $firstOfID = false;
+
+	public $changes;
+
+	function __construct($type) {
+		$this->type = $type;
+	}
+
+	public static function typeToString($type) {
+		switch($type) {
+			case self::NONE: return 'none';
+			case self::REMOVED: return 'removed';
+			case self::ADDED: return 'added';
+			case self::CHANGED: return 'changed';
+		}
+	}
+}
+
+class DomTreeBuilder {
+
+	public $textNodes = array();
+
+	public $bodyNode;
+
+	private $currentParent;
+
+	private $newWord = '';
+
+	protected $bodyStarted = false;
+
+	protected $bodyEnded = false;
+
+	private $whiteSpaceBeforeThis = false;
+
+	private $lastSibling;
+
+	private $notInPre = true;
+
+	function __construct() {
+		$this->bodyNode = $this->currentParent = new BodyNode();
+		$this->lastSibling = new DummyNode();
+	}
+
+	/**
+	 * Must be called manually
+	 */
+	public function endDocument() {
+		$this->endWord();
+		HTMLDiffer::diffDebug( count($this->textNodes) . " text nodes in document.\n" );
+	}
+
+	public function startElement($parser, $name, /*array*/ $attributes) {
+		if (strcasecmp($name, 'body') != 0) {
+			HTMLDiffer::diffDebug( "Starting $name node.\n" );
+			$this->endWord();
+
+			$newNode = new TagNode($this->currentParent, $name, $attributes);
+			$this->currentParent->children[] = $newNode;
+			$this->currentParent = $newNode;
+			$this->lastSibling = new DummyNode();
+			if ($this->whiteSpaceBeforeThis && !in_array(strtolower($this->currentParent->qName),TagNode::$blocks)) {
+				$this->currentParent->whiteBefore = true;
+			}
+			$this->whiteSpaceBeforeThis = false;
+			if(strcasecmp($name, 'pre') == 0) {
+				$this->notInPre = false;
+			}
+		}
+	}
+
+	public function endElement($parser, $name) {
+		if(strcasecmp($name, 'body') != 0) {
+			HTMLDiffer::diffDebug( "Ending $name node.\n");
+			if (0 == strcasecmp($name,'img')) {
+				// Insert a dummy leaf for the image
+				$img = new ImageNode($this->currentParent, $this->currentParent->attributes);
+				$this->currentParent->children[] = $img;
+				$img->whiteBefore = $this->whiteSpaceBeforeThis;
+				$this->lastSibling = $img;
+				$this->textNodes[] = $img;
+			}
+			$this->endWord();
+			if (!in_array(strtolower($this->currentParent->qName),TagNode::$blocks)) {
+				$this->lastSibling = $this->currentParent;
+			} else {
+				$this->lastSibling = new DummyNode();
+			}
+			$this->currentParent = $this->currentParent->parent;
+			$this->whiteSpaceBeforeThis = false;
+			if (!$this->notInPre && strcasecmp($name, 'pre') == 0) {
+				$this->notInPre = true;
+			}
+		} else {
+			$this->endDocument();
+		}
+	}
+
+	const regex = '/([\s\.\,\"\\\'\(\)\?\:\;\!\{\}\-\+\*\=\_\[\]\&\|\$]{1})/';
+	const whitespace = '/^[\s]{1}$/';
+	const delimiter = '/^[\s\.\,\"\\\'\(\)\?\:\;\!\{\}\-\+\*\=\_\[\]\&\|\$]{1}$/';
+
+	public function characters($parser, $data) {
+		$matches = preg_split(self::regex, $data, -1, PREG_SPLIT_DELIM_CAPTURE);
+
+		foreach($matches as &$word) {
+			if (preg_match(self::whitespace, $word) && $this->notInPre) {
+				$this->endWord();
+				$this->lastSibling->whiteAfter = true;
+				$this->whiteSpaceBeforeThis = true;
+			} else if (preg_match(self::delimiter, $word)) {
+				$this->endWord();
+				$textNode = new TextNode($this->currentParent, $word);
+				$this->currentParent->children[] = $textNode;
+				$textNode->whiteBefore = $this->whiteSpaceBeforeThis;
+				$this->whiteSpaceBeforeThis = false;
+				$this->lastSibling = $textNode;
+				$this->textNodes[] = $textNode;
+			} else {
+				$this->newWord .= $word;
+			}
+		}
+	}
+
+	private function endWord() {
+		if ($this->newWord !== '') {
+			$node = new TextNode($this->currentParent, $this->newWord);
+			$this->currentParent->children[] = $node;
+			$node->whiteBefore = $this->whiteSpaceBeforeThis;
+			$this->whiteSpaceBeforeThis = false;
+			$this->lastSibling = $node;
+			$this->textNodes[] = $node;
+			$this->newWord = "";
+		}
+	}
+
+	public function getDiffLines() {
+		return array_map(array('TextNode','toDiffLine'), $this->textNodes);
+	}
+}
+
+class TextNodeDiffer {
+
+	private $textNodes;
+	public $bodyNode;
+
+	private $oldTextNodes;
+	private $oldBodyNode;
+
+	private $newID = 0;
+
+	private $changedID = 0;
+
+	private $changedIDUsed = false;
+
+	// used to remove the whitespace between a red and green block
+	private $whiteAfterLastChangedPart = false;
+
+	private $deletedID = 0;
+
+	function __construct(DomTreeBuilder $tree, DomTreeBuilder $oldTree) {
+		$this->textNodes = $tree->textNodes;
+		$this->bodyNode = $tree->bodyNode;
+		$this->oldTextNodes = $oldTree->textNodes;
+		$this->oldBodyNode = $oldTree->bodyNode;
+	}
+
+	public function markAsNew($start, $end) {
+		if ($end <= $start) {
+			return;
+		}
+
+		if ($this->whiteAfterLastChangedPart) {
+			$this->textNodes[$start]->whiteBefore = false;
+		}
+
+		for ($i = $start; $i < $end; ++$i) {
+			$mod = new Modification(Modification::ADDED);
+			$mod->id = $this->newID;
+			$this->textNodes[$i]->modification = $mod;
+		}
+		if ($start < $end) {
+			$this->textNodes[$start]->modification->firstOfID = true;
+		}
+		++$this->newID;
+	}
+
+	public function handlePossibleChangedPart($leftstart, $leftend,	$rightstart, $rightend) {
+		$i = $rightstart;
+		$j = $leftstart;
+
+		if ($this->changedIDUsed) {
+			++$this->changedID;
+			$this->changedIDUsed = false;
+		}
+
+		$changes;
+		while ($i < $rightend) {
+			$acthis = new AncestorComparator($this->textNodes[$i]->getParentTree());
+			$acother = new AncestorComparator($this->oldTextNodes[$j]->getParentTree());
+			$result = $acthis->getResult($acother);
+			unset($acthis, $acother);
+
+			if ( $result ) {
+				$mod = new Modification(Modification::CHANGED);
+
+				if (!$this->changedIDUsed) {
+					$mod->firstOfID = true;
+				} else if (!is_null( $result ) && $result !== $this->changes) {
+					++$this->changedID;
+					$mod->firstOfID = true;
+				}
+
+				$mod->changes = $result;
+				$mod->id = $this->changedID;
+
+				$this->textNodes[$i]->modification = $mod;
+				$this->changes = $result;
+				$this->changedIDUsed = true;
+			} else if ($this->changedIDUsed) {
+				++$this->changedID;
+				$this->changedIDUsed = false;
+			}
+			++$i;
+			++$j;
+		}
+	}
+
+	public function markAsDeleted($start, $end, $before) {
+
+		if ($end <= $start) {
+			return;
+		}
+
+		if ($before > 0 && $this->textNodes[$before - 1]->whiteAfter) {
+			$this->whiteAfterLastChangedPart = true;
+		} else {
+			$this->whiteAfterLastChangedPart = false;
+		}
+
+		for ($i = $start; $i < $end; ++$i) {
+			$mod = new Modification(Modification::REMOVED);
+			$mod->id = $this->deletedID;
+
+			// oldTextNodes is used here because we're going to move its deleted
+			// elements to this tree!
+			$this->oldTextNodes[$i]->modification = $mod;
+		}
+		$this->oldTextNodes[$start]->modification->firstOfID = true;
+
+		$root = $this->oldTextNodes[$start]->getLastCommonParent($this->oldTextNodes[$end-1])->parent;
+
+		$junk1 = $junk2 = null;
+		$deletedNodes = $root->getMinimalDeletedSet($this->deletedID, $junk1, $junk2);
+
+		HTMLDiffer::diffDebug( "Minimal set of deleted nodes of size " . count($deletedNodes) . "\n" );
+
+		// Set prevLeaf to the leaf after which the old HTML needs to be
+		// inserted
+		if ($before > 0) {
+			$prevLeaf = $this->textNodes[$before - 1];
+		}
+		// Set nextLeaf to the leaf before which the old HTML needs to be
+		// inserted
+		if ($before < count($this->textNodes)) {
+			$nextLeaf = $this->textNodes[$before];
+		}
+
+		while (count($deletedNodes) > 0) {
+			if (isset($prevLeaf)) {
+				$prevResult = $prevLeaf->getLastCommonParent($deletedNodes[0]);
+			} else {
+				$prevResult = new LastCommonParentResult();
+				$prevResult->parent = $this->bodyNode;
+				$prevResult->indexInLastCommonParent = -1;
+			}
+			if (isset($nextleaf)) {
+				$nextResult = $nextLeaf->getLastCommonParent($deletedNodes[count($deletedNodes) - 1]);
+			} else {
+				$nextResult = new LastCommonParentResult();
+				$nextResult->parent = $this->bodyNode;
+				$nextResult->indexInLastCommonParent = $this->bodyNode->getNbChildren();
+			}
+
+			if ($prevResult->lastCommonParentDepth == $nextResult->lastCommonParentDepth) {
+				// We need some metric to choose which way to add-...
+				if ($deletedNodes[0]->parent === $deletedNodes[count($deletedNodes) - 1]->parent
+						&& $prevResult->parent === $nextResult->parent) {
+					// The difference is not in the parent
+					$prevResult->lastCommonParentDepth = $prevResult->lastCommonParentDepth + 1;
+				} else {
+					// The difference is in the parent, so compare them
+					// now THIS is tricky
+					$distancePrev = $deletedNodes[0]->parent->getMatchRatio($prevResult->parent);
+					$distanceNext = $deletedNodes[count($deletedNodes) - 1]->parent->getMatchRatio($nextResult->parent);
+
+					if ($distancePrev <= $distanceNext) {
+						$prevResult->lastCommonParentDepth = $prevResult->lastCommonParentDepth + 1;
+					} else {
+						$nextResult->lastCommonParentDepth = $nextResult->lastCommonParentDepth + 1;
+					}
+				}
+
+			}
+
+			if ($prevResult->lastCommonParentDepth > $nextResult->lastCommonParentDepth) {
+				// Inserting at the front
+				if ($prevResult->splittingNeeded) {
+					$prevLeaf->parent->splitUntil($prevResult->parent, $prevLeaf, true);
+				}
+				$prevLeaf = $deletedNodes[0]->copyTree();
+				unset($deletedNodes[0]);
+				$deletedNodes = array_values($deletedNodes);
+				$prevLeaf->setParent($prevResult->parent);
+				$prevResult->parent->addChildAbsolute($prevLeaf,$prevResult->indexInLastCommonParent + 1);
+			} else if ($prevResult->lastCommonParentDepth < $nextResult->lastCommonParentDepth) {
+				// Inserting at the back
+				if ($nextResult->splittingNeeded) {
+					$splitOccured = $nextLeaf->parent->splitUntil($nextResult->parent, $nextLeaf, false);
+					if ($splitOccured) {
+						// The place where to insert is shifted one place to the
+						// right
+						$nextResult->indexInLastCommonParent = $nextResult->indexInLastCommonParent + 1;
+					}
+				}
+				$nextLeaf = $deletedNodes[count(deletedNodes) - 1]->copyTree();
+				unset($deletedNodes[count(deletedNodes) - 1]);
+				$deletedNodes = array_values($deletedNodes);
+				$nextLeaf->setParent($nextResult->parent);
+				$nextResult->parent->addChildAbsolute($nextLeaf,$nextResult->indexInLastCommonParent);
+			}
+		}
+		++$this->deletedID;
+	}
+
+	public function expandWhiteSpace() {
+		$this->bodyNode->expandWhiteSpace();
+	}
+
+	public function lengthNew(){
+		return count($this->textNodes);
+	}
+
+	public function lengthOld(){
+		return count($this->oldTextNodes);
+	}
+}
+
+class HTMLDiffer {
+
+	private $output;
+	private static $debug = '';
+
+	function __construct($output) {
+		$this->output = $output;
+	}
+
+	function htmlDiff($from, $to) {
+		wfProfileIn( __METHOD__ );
+		// Create an XML parser
+		$xml_parser = xml_parser_create('');
+
+		$domfrom = new DomTreeBuilder();
+
+		// Set the functions to handle opening and closing tags
+		xml_set_element_handler($xml_parser, array($domfrom, "startElement"), array($domfrom, "endElement"));
+
+		// Set the function to handle blocks of character data
+		xml_set_character_data_handler($xml_parser, array($domfrom, "characters"));
+
+		HTMLDiffer::diffDebug( "Parsing " . strlen($from) . " characters worth of HTML\n" );
+		if (!xml_parse($xml_parser, '<?xml version="1.0" encoding="UTF-8"?>'.Sanitizer::hackDocType().'<body>', false)
+					|| !xml_parse($xml_parser, $from, false)
+					|| !xml_parse($xml_parser, '</body>', true)){
+			$error = xml_error_string(xml_get_error_code($xml_parser));
+			$line = xml_get_current_line_number($xml_parser);
+			HTMLDiffer::diffDebug( "XML error: $error at line $line\n" );
+		}
+		xml_parser_free($xml_parser);
+		unset($from);
+
+		$xml_parser = xml_parser_create('');
+
+		$domto = new DomTreeBuilder();
+
+		// Set the functions to handle opening and closing tags
+		xml_set_element_handler($xml_parser, array($domto, "startElement"), array($domto, "endElement"));
+
+		// Set the function to handle blocks of character data
+		xml_set_character_data_handler($xml_parser, array($domto, "characters"));
+
+		HTMLDiffer::diffDebug( "Parsing " . strlen($to) . " characters worth of HTML\n" );
+		if (!xml_parse($xml_parser, '<?xml version="1.0" encoding="UTF-8"?>'.Sanitizer::hackDocType().'<body>', false)
+		|| !xml_parse($xml_parser, $to, false)
+		|| !xml_parse($xml_parser, '</body>', true)){
+			$error = xml_error_string(xml_get_error_code($xml_parser));
+			$line = xml_get_current_line_number($xml_parser);
+			HTMLDiffer::diffDebug( "XML error: $error at line $line\n" );
+		}
+		xml_parser_free($xml_parser);
+		unset($to);
+
+		$diffengine = new WikiDiff3();
+		$differences = $this->preProcess($diffengine->diff_range($domfrom->getDiffLines(), $domto->getDiffLines()));
+		unset($xml_parser, $diffengine);
+
+		$domdiffer = new TextNodeDiffer($domto, $domfrom);
+
+		$currentIndexLeft = 0;
+		$currentIndexRight = 0;
+		foreach ($differences as &$d) {
+			if ($d->leftstart > $currentIndexLeft) {
+				$domdiffer->handlePossibleChangedPart($currentIndexLeft, $d->leftstart,
+					$currentIndexRight, $d->rightstart);
+			}
+			if ($d->leftlength > 0) {
+				$domdiffer->markAsDeleted($d->leftstart, $d->leftend, $d->rightstart);
+			}
+			$domdiffer->markAsNew($d->rightstart, $d->rightend);
+
+			$currentIndexLeft = $d->leftend;
+			$currentIndexRight = $d->rightend;
+		}
+		$oldLength = $domdiffer->lengthOld();
+		if ($currentIndexLeft < $oldLength) {
+			$domdiffer->handlePossibleChangedPart($currentIndexLeft, $oldLength, $currentIndexRight, $domdiffer->lengthNew());
+		}
+		$domdiffer->expandWhiteSpace();
+		$output = new HTMLOutput('htmldiff', $this->output);
+		$output->parse($domdiffer->bodyNode);
+		wfProfileOut( __METHOD__ );
+	}
+
+	private function preProcess(/*array*/ $differences) {
+		$newRanges = array();
+
+		$nbDifferences = count($differences);
+		for ($i = 0; $i < $nbDifferences; ++$i) {
+			$leftStart = $differences[$i]->leftstart;
+			$leftEnd = $differences[$i]->leftend;
+			$rightStart = $differences[$i]->rightstart;
+			$rightEnd = $differences[$i]->rightend;
+
+			$leftLength = $leftEnd - $leftStart;
+			$rightLength = $rightEnd - $rightStart;
+
+			while ($i + 1 < $nbDifferences && self::score($leftLength,
+						$differences[$i + 1]->leftlength,
+						$rightLength,
+						$differences[$i + 1]->rightlength)
+					> ($differences[$i + 1]->leftstart - $leftEnd)) {
+				$leftEnd = $differences[$i + 1]->leftend;
+				$rightEnd = $differences[$i + 1]->rightend;
+				$leftLength = $leftEnd - $leftStart;
+				$rightLength = $rightEnd - $rightStart;
+				++$i;
+			}
+			$newRanges[] = new RangeDifference($leftStart, $leftEnd, $rightStart, $rightEnd);
+		}
+		return $newRanges;
+	}
+
+	/**
+	 * Heuristic to merge differences for readability.
+	 */
+	public static function score($ll, $nll, $rl, $nrl) {
+		if (($ll == 0 && $nll == 0)
+				|| ($rl == 0 && $nrl == 0)) {
+			return 0;
+		}
+		$numbers = array($ll, $nll, $rl, $nrl);
+		$d = 0;
+		foreach ($numbers as &$number) {
+			while ($number > 3) {
+				$d += 3;
+				$number -= 3;
+				$number *= 0.5;
+			}
+			$d += $number;
+
+		}
+		return $d / (1.5 * count($numbers));
+	}
+
+	/**
+	 * Add to debug output
+	 * @param string $str Debug output
+	 */
+	public static function diffDebug( $str ) {
+		self :: $debug .= $str;
+	}
+	
+	/**
+	 * Get debug output
+	 * @return string
+	 */
+	public static function getDebugOutput() {
+		return self :: $debug;
+	}
+
+}
+
+class TextOnlyComparator {
+
+	public $leafs = array();
+
+	function _construct(TagNode $tree) {
+		$this->addRecursive($tree);
+		$this->leafs = array_map(array('TextNode','toDiffLine'), $this->leafs);
+	}
+
+	private function addRecursive(TagNode $tree) {
+		foreach ($tree->children as &$child) {
+			if ($child instanceof TagNode) {
+				$this->addRecursive($child);
+			} else if ($child instanceof TextNode) {
+				$this->leafs[] = $node;
+			}
+		}
+	}
+
+	public function getMatchRatio(TextOnlyComparator $other) {
+		$nbOthers = count($other->leafs);
+		$nbThis = count($this->leafs);
+		if($nbOthers == 0 || $nbThis == 0){
+			return -log(0);
+		}
+
+		$diffengine = new WikiDiff3(25000, 1.35);
+		$diffengine->diff($this->leafs, $other->leafs);
+
+		$lcsLength = $diffengine->getLcsLength();
+
+		$distanceThis = $nbThis-$lcsLength;
+
+		return (2.0 - $lcsLength/$nbOthers - $lcsLength/$nbThis) / 2.0;
+	}
+}
+
+/**
+ * A comparator used when calculating the difference in ancestry of two Nodes.
+ */
+class AncestorComparator {
+
+	public $ancestors;
+	public $ancestorsText;
+
+	function __construct(/*array*/ $ancestors) {
+		$this->ancestors = $ancestors;
+		$this->ancestorsText = array_map(array('TagNode','toDiffLine'), $ancestors);
+	}
+
+	public $compareTxt = "";
+
+	public function getResult(AncestorComparator $other) {
+
+		$diffengine = new WikiDiff3(10000, 1.35);
+		$differences = $diffengine->diff_range($other->ancestorsText,$this->ancestorsText);
+
+		if (count($differences) == 0){
+			return null;
+		}
+		$changeTxt = new ChangeTextGenerator($this, $other);
+
+		return $changeTxt->getChanged($differences)->toString();;
+	}
+}
+
+class ChangeTextGenerator {
+
+	private $ancestorComparator;
+	private $other;
+
+	private $factory;
+
+	function __construct(AncestorComparator $ancestorComparator, AncestorComparator $other) {
+		$this->ancestorComparator = $ancestorComparator;
+		$this->other = $other;
+		$this->factory = new TagToStringFactory();
+	}
+
+	public function getChanged(/*array*/ $differences) {
+		$txt = new ChangeText;
+		$rootlistopened = false;
+		if (count($differences) > 1) {
+			$txt->addHtml('<ul class="changelist">');
+			$rootlistopened = true;
+		}
+		$nbDifferences = count($differences);
+		for ($j = 0; $j < $nbDifferences; ++$j) {
+			$d = $differences[$j];
+			$lvl1listopened = false;
+			if ($rootlistopened) {
+				$txt->addHtml('<li>');
+			}
+			if ($d->leftlength + $d->rightlength > 1) {
+				$txt->addHtml('<ul class="changelist">');
+				$lvl1listopened = true;
+			}
+			// left are the old ones
+			for ($i = $d->leftstart; $i < $d->leftend; ++$i) {
+				if ($lvl1listopened){
+					$txt->addHtml('<li>');
+				}
+				// add a bullet for a old tag
+				$this->addTagOld($txt, $this->other->ancestors[$i]);
+				if ($lvl1listopened){
+					$txt->addHtml('</li>');
+				}
+			}
+			// right are the new ones
+			for ($i = $d->rightstart; $i < $d->rightend; ++$i) {
+				if ($lvl1listopened){
+					$txt->addHtml('<li>');
+				}
+				// add a bullet for a new tag
+				$this->addTagNew($txt, $this->ancestorComparator->ancestors[$i]);
+
+				if ($lvl1listopened){
+					$txt->addHtml('</li>');
+				}
+			}
+			if ($lvl1listopened) {
+				$txt->addHtml('</ul>');
+			}
+			if ($rootlistopened) {
+				$txt->addHtml('</li>');
+			}
+		}
+		if ($rootlistopened) {
+			$txt->addHtml('</ul>');
+		}
+		return $txt;
+	}
+
+	private function addTagOld(ChangeText $txt, TagNode $ancestor) {
+		$this->factory->create($ancestor)->getRemovedDescription($txt);
+	}
+
+	private function addTagNew(ChangeText $txt, TagNode $ancestor) {
+		$this->factory->create($ancestor)->getAddedDescription($txt);
+	}
+}
+
+class ChangeText {
+
+	private $txt = "";
+
+	public function addHtml($s) {
+		$this->txt .= $s;
+	}
+
+	public function toString() {
+		return $this->txt;
+	}
+}
+
+class TagToStringFactory {
+
+	private static $containerTags = array('html', 'body', 'p', 'blockquote',
+		'h1', 'h2', 'h3', 'h4', 'h5', 'pre', 'div', 'ul', 'ol', 'li',
+		'table', 'tbody', 'tr', 'td', 'th', 'br', 'hr', 'code', 'dl',
+		'dt', 'dd', 'input', 'form', 'img', 'span', 'a');
+
+	private static $styleTags = array('i', 'b', 'strong', 'em', 'font',
+		'big', 'del', 'tt', 'sub', 'sup', 'strike');
+
+	const MOVED = 1;
+	const STYLE = 2;
+	const UNKNOWN = 4;
+
+	public function create(TagNode $node) {
+		$sem = $this->getChangeSemantic($node->qName);
+		if (strcasecmp($node->qName,'a') == 0) {
+			return new AnchorToString($node, $sem);
+		}
+		if (strcasecmp($node->qName,'img') == 0) {
+			return new NoContentTagToString($node, $sem);
+		}
+		return new TagToString($node, $sem);
+	}
+
+	protected function getChangeSemantic($qname) {
+		if (in_array(strtolower($qname),self::$containerTags)) {
+			return self::MOVED;
+		}
+		if (in_array(strtolower($qname),self::$styleTags)) {
+			return self::STYLE;
+		}
+		return self::UNKNOWN;
+	}
+}
+
+class TagToString {
+
+	protected $node;
+
+	protected $sem;
+
+	function __construct(TagNode $node, $sem) {
+		$this->node = $node;
+		$this->sem = $sem;
+	}
+
+	public function getRemovedDescription(ChangeText $txt) {
+		$tagDescription = wfMsgExt('diff-' . $this->node->qName, 'parseinline' );
+		if( wfEmptyMsg( 'diff-' . $this->node->qName, $tagDescription ) ){
+			$tagDescription = "&lt;" . $this->node->qName . "&gt;";
+		}
+		if ($this->sem == TagToStringFactory::MOVED) {
+			$txt->addHtml( wfMsgExt( 'diff-movedoutof', 'parseinline', $tagDescription ) );
+		} else if ($this->sem == TagToStringFactory::STYLE) {
+			$txt->addHtml( wfMsgExt( 'diff-styleremoved' , 'parseinline', $tagDescription ) );
+		} else {
+			$txt->addHtml( wfMsgExt( 'diff-removed' , 'parseinline', $tagDescription ) );
+		}
+		$this->addAttributes($txt, $this->node->attributes);
+		$txt->addHtml('.');
+	}
+
+	public function getAddedDescription(ChangeText $txt) {
+		$tagDescription = wfMsgExt('diff-' . $this->node->qName, 'parseinline' );
+		if( wfEmptyMsg( 'diff-' . $this->node->qName, $tagDescription ) ){
+			$tagDescription = "&lt;" . $this->node->qName . "&gt;";
+		}
+		if ($this->sem == TagToStringFactory::MOVED) {
+			$txt->addHtml( wfMsgExt( 'diff-movedto' , 'parseinline', $tagDescription) );
+		} else if ($this->sem == TagToStringFactory::STYLE) {
+			$txt->addHtml( wfMsgExt( 'diff-styleadded', 'parseinline', $tagDescription ) );
+		} else {
+			$txt->addHtml( wfMsgExt( 'diff-added', 'parseinline', $tagDescription ) );
+		}
+		$this->addAttributes($txt, $this->node->attributes);
+		$txt->addHtml('.');
+	}
+
+	protected function addAttributes(ChangeText $txt, array $attributes) {
+		if (count($attributes) < 1) {
+			return;
+		}
+		$firstOne = true;
+		$nbAttributes_min_1 = count($attributes)-1;
+		$keys = array_keys($attributes);
+		for ($i=0;$i<$nbAttributes_min_1;$i++) {
+			$key = $keys[$i];
+			$attr = $attributes[$key];
+			if($firstOne) {
+				$firstOne = false;
+				$txt->addHtml( wfMsgExt('diff-with', 'escapenoentities', $this->translateArgument($key), htmlspecialchars($attr) ) );
+				continue;
+			}
+			$txt->addHtml( wfMsgExt( 'comma-separator', 'escapenoentities' ) .
+				wfMsgExt( 'diff-with-additional', 'escapenoentities',
+				$this->translateArgument( $key ), htmlspecialchars( $attr ) )
+			);
+		}
+
+		if ($nbAttributes_min_1 > 0) {
+			$txt->addHtml( wfMsgExt( 'diff-with-final', 'escapenoentities',
+			$this->translateArgument($keys[$nbAttributes_min_1]),
+			htmlspecialchars($attributes[$keys[$nbAttributes_min_1]]) ) );
+		}
+	}
+
+	protected function translateArgument($name) {
+		$translation = wfMsgExt('diff-' . $name, 'parseinline' );
+		if ( wfEmptyMsg( 'diff-' . $name, $translation ) ) {
+			$translation = "&lt;" . $name . "&gt;";;
+		}
+		return htmlspecialchars( $translation );
+	}
+}
+
+class NoContentTagToString extends TagToString {
+
+	function __construct(TagNode $node, $sem) {
+		parent::__construct($node, $sem);
+	}
+
+	public function getAddedDescription(ChangeText $txt) {
+		$tagDescription = wfMsgExt('diff-' . $this->node->qName, 'parseinline' );
+		if( wfEmptyMsg( 'diff-' . $this->node->qName, $tagDescription ) ){
+			$tagDescription = "&lt;" . $this->node->qName . "&gt;";
+		}
+		$txt->addHtml( wfMsgExt('diff-changedto', 'parseinline', $tagDescription ) );
+		$this->addAttributes($txt, $this->node->attributes);
+		$txt->addHtml('.');
+	}
+
+	public function getRemovedDescription(ChangeText $txt) {
+		$txt->addHtml( wfMsgExt('diff-changedfrom', 'parseinline', $tagDescription ) );
+		$this->addAttributes($txt, $this->node->attributes);
+		$txt->addHtml('.');
+	}
+}
+
+class AnchorToString extends TagToString {
+
+	function __construct(TagNode $node, $sem) {
+		parent::__construct($node, $sem);
+	}
+
+	protected function addAttributes(ChangeText $txt, array $attributes) {
+		if (array_key_exists('href', $attributes)) {
+			$txt->addHtml(' ' . wfMsgExt( 'diff-withdestination', 'parseinline', htmlspecialchars($attributes['href']) ) );
+			unset($attributes['href']);
+		}
+		parent::addAttributes($txt, $attributes);
+	}
+}
+
+/**
+ * Takes a branch root and creates an HTML file for it.
+ */
+class HTMLOutput{
+
+	private $prefix;
+	private $handler;
+
+	function __construct($prefix, $handler) {
+		$this->prefix = $prefix;
+		$this->handler = $handler;
+	}
+
+	public function parse(TagNode $node) {
+		$handler = &$this->handler;
+
+		if (strcasecmp($node->qName, 'img') != 0 && strcasecmp($node->qName, 'body') != 0) {
+			$handler->startElement($node->qName, $node->attributes);
+		}
+
+		$newStarted = false;
+		$remStarted = false;
+		$changeStarted = false;
+		$changeTXT = '';
+
+		foreach ($node->children as &$child) {
+			if ($child instanceof TagNode) {
+				if ($newStarted) {
+					$handler->endElement('span');
+					$newStarted = false;
+				} else if ($changeStarted) {
+					$handler->endElement('span');
+					$changeStarted = false;
+				} else if ($remStarted) {
+					$handler->endElement('span');
+					$remStarted = false;
+				}
+				$this->parse($child);
+			} else if ($child instanceof TextNode) {
+				$mod = $child->modification;
+
+				if ($newStarted && ($mod->type != Modification::ADDED || $mod->firstOfID)) {
+					$handler->endElement('span');
+					$newStarted = false;
+				} else if ($changeStarted && ($mod->type != Modification::CHANGED
+						|| $mod->changes != $changeTXT || $mod->firstOfID)) {
+					$handler->endElement('span');
+					$changeStarted = false;
+				} else if ($remStarted && ($mod->type != Modification::REMOVED || $mod ->firstOfID)) {
+					$handler->endElement('span');
+					$remStarted = false;
+				}
+
+				// no else because a removed part can just be closed and a new
+				// part can start
+				if (!$newStarted && $mod->type == Modification::ADDED) {
+					$attrs = array('class' => 'diff-html-added');
+					if ($mod->firstOfID) {
+						$attrs['id'] = "added-{$this->prefix}-{$mod->id}";
+					}
+					$handler->startElement('span', $attrs);
+					$newStarted = true;
+				} else if (!$changeStarted && $mod->type == Modification::CHANGED) {
+					$attrs = array('class' => 'diff-html-changed');
+					if ($mod->firstOfID) {
+						$attrs['id'] = "changed-{$this->prefix}-{$mod->id}";
+					}
+					$handler->startElement('span', $attrs);
+
+					//tooltip
+					$handler->startElement('span', array('class' => 'tip'));
+					$handler->html($mod->changes);
+					$handler->endElement('span');
+
+					$changeStarted = true;
+					$changeTXT = $mod->changes;
+				} else if (!$remStarted && $mod->type == Modification::REMOVED) {
+					$attrs = array('class'=>'diff-html-removed');
+					if ($mod->firstOfID) {
+						$attrs['id'] = "removed-{$this->prefix}-{$mod->id}";
+					}
+					$handler->startElement('span', $attrs);
+					$remStarted = true;
+				}
+
+				$chars = $child->text;
+
+				if ($child instanceof ImageNode) {
+					$this->writeImage($child);
+				} else {
+					$handler->characters($chars);
+				}
+			}
+		}
+
+		if ($newStarted) {
+			$handler->endElement('span');
+			$newStarted = false;
+		} else if ($changeStarted) {
+			$handler->endElement('span');
+			$changeStarted = false;
+		} else if ($remStarted) {
+			$handler->endElement('span');
+			$remStarted = false;
+		}
+
+		if (strcasecmp($node->qName, 'img') != 0
+				&& strcasecmp($node->qName, 'body') != 0) {
+			$handler->endElement($node->qName);
+		}
+	}
+
+	private function writeImage(ImageNode  $imgNode) {
+		$attrs = $imgNode->attributes;
+		$this->handler->startElement('img', $attrs);
+		$this->handler->endElement('img');
+	}
+}
+
+class DelegatingContentHandler {
+
+	private $delegate;
+
+	function __construct($delegate) {
+		$this->delegate = $delegate;
+	}
+
+	function startElement($qname, /*array*/ $arguments) {
+		$this->delegate->addHtml(Xml::openElement($qname, $arguments));
+	}
+
+	function endElement($qname){
+		$this->delegate->addHtml(Xml::closeElement($qname));
+	}
+
+	function characters($chars){
+		$this->delegate->addHtml(htmlspecialchars($chars));
+	}
+
+	function html($html){
+		$this->delegate->addHtml($html);
+	}
+}
diff --git a/includes/diff/Nodes.php b/includes/diff/Nodes.php
new file mode 100644
index 00000000..1b1363d4
--- /dev/null
+++ b/includes/diff/Nodes.php
@@ -0,0 +1,439 @@
+<?php
+
+/** Copyright (C) 2008 Guy Van den Broeck <guy@guyvdb.eu>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
+ * or see http://www.gnu.org/
+ * 
+ */
+ 
+/**
+ * Any element in the DOM tree of an HTML document.
+ * @ingroup DifferenceEngine
+ */
+class Node {
+
+	public $parent;
+
+	protected $parentTree;
+
+	public $whiteBefore = false;
+
+	public $whiteAfter = false;
+
+	function __construct($parent) {
+		$this->parent = $parent;
+	}
+
+	public function getParentTree() {
+		if (!isset($this->parentTree)) {
+			if (!is_null($this->parent)) {
+				$this->parentTree = $this->parent->getParentTree();
+				$this->parentTree[] = $this->parent;
+			} else {
+				$this->parentTree = array();
+			}
+		}
+		return $this->parentTree;
+	}
+
+	public function getLastCommonParent(Node $other) {
+		$result = new LastCommonParentResult();
+
+		$myParents = $this->getParentTree();
+		$otherParents = $other->getParentTree();
+
+		$i = 1;
+		$isSame = true;
+		$nbMyParents = count($myParents);
+		$nbOtherParents = count($otherParents);
+		while ($isSame && $i < $nbMyParents && $i < $nbOtherParents) {
+			if (!$myParents[$i]->openingTag === $otherParents[$i]->openingTag) {
+				$isSame = false;
+			} else {
+				// After a while, the index i-1 must be the last common parent
+				$i++;
+			}
+		}
+
+		$result->lastCommonParentDepth = $i - 1;
+		$result->parent = $myParents[$i - 1];
+
+		if (!$isSame || $nbMyParents > $nbOtherParents) {
+			// Not all tags matched, or all tags matched but
+			// there are tags left in this tree
+			$result->indexInLastCommonParent = $myParents[$i - 1]->getIndexOf($myParents[$i]);
+			$result->splittingNeeded = true;
+		} else if ($nbMyParents <= $nbOtherParents) {
+			$result->indexInLastCommonParent = $myParents[$i - 1]->getIndexOf($this);
+		}
+		return $result;
+	}
+
+	public function setParent($parent) {
+		$this->parent = $parent;
+		unset($this->parentTree);
+	}
+
+	public function inPre() {
+		$tree = $this->getParentTree();
+		foreach ($tree as &$ancestor) {
+			if ($ancestor->isPre()) {
+				return true;
+			}
+		}
+		return false;
+	}
+}
+
+/**
+ * Node that can contain other nodes. Represents an HTML tag.
+ * @ingroup DifferenceEngine
+ */
+class TagNode extends Node {
+
+	public $children = array();
+
+	public $qName;
+
+	public $attributes = array();
+
+	public $openingTag;
+
+	function __construct($parent, $qName, /*array*/ $attributes) {
+		parent::__construct($parent);
+		$this->qName = strtolower($qName);
+		foreach($attributes as $key => &$value){
+			$this->attributes[strtolower($key)] = $value;
+		}
+		return $this->openingTag = Xml::openElement($this->qName, $this->attributes);
+	}
+
+	public function addChildAbsolute(Node $node, $index) {
+		array_splice($this->children, $index, 0, array($node));
+	}
+
+	public function getIndexOf(Node $child) {
+		// don't trust array_search with objects
+		foreach ($this->children as $key => &$value){
+			if ($value === $child) {
+				return $key;
+			}
+		}
+		return null;
+	}
+
+	public function getNbChildren() {
+		return count($this->children);
+	}
+
+	public function getMinimalDeletedSet($id, &$allDeleted, &$somethingDeleted) {
+		$nodes = array();
+
+		$allDeleted = false;
+		$somethingDeleted = false;
+		$hasNonDeletedDescendant = false;
+
+		if (empty($this->children)) {
+			return $nodes;
+		}
+
+		foreach ($this->children as &$child) {
+			$allDeleted_local = false;
+			$somethingDeleted_local = false;
+			$childrenChildren = $child->getMinimalDeletedSet($id, $allDeleted_local, $somethingDeleted_local);
+			if ($somethingDeleted_local) {
+				$nodes = array_merge($nodes, $childrenChildren);
+				$somethingDeleted = true;
+			}
+			if (!$allDeleted_local) {
+				$hasNonDeletedDescendant = true;
+			}
+		}
+		if (!$hasNonDeletedDescendant) {
+			$nodes = array($this);
+			$allDeleted = true;
+		}
+		return $nodes;
+	}
+
+	public function splitUntil(TagNode $parent, Node $split, $includeLeft) {
+		$splitOccured = false;
+		if ($parent !== $this) {
+			$part1 = new TagNode(null, $this->qName, $this->attributes);
+			$part2 = new TagNode(null, $this->qName, $this->attributes);
+			$part1->setParent($this->parent);
+			$part2->setParent($this->parent);
+
+			$onSplit = false;
+			$pastSplit = false;
+			foreach ($this->children as &$child)
+			{
+				if ($child === $split) {
+					$onSplit = true;
+				}
+				if(!$pastSplit || ($onSplit && $includeLeft)) {
+					$child->setParent($part1);
+					$part1->children[] = $child;
+				} else {
+					$child->setParent($part2);
+					$part2->children[] = $child;
+				}
+				if ($onSplit) {
+					$onSplit = false;
+					$pastSplit = true;
+				}
+			}
+			$myindexinparent = $this->parent->getIndexOf($this);
+			if (!empty($part1->children)) {
+				$this->parent->addChildAbsolute($part1, $myindexinparent);
+			}
+			if (!empty($part2->children)) {
+				$this->parent->addChildAbsolute($part2, $myindexinparent);
+			}
+			if (!empty($part1->children) && !empty($part2->children)) {
+				$splitOccured = true;
+			}
+
+			$this->parent->removeChild($myindexinparent);
+
+			if ($includeLeft) {
+				$this->parent->splitUntil($parent, $part1, $includeLeft);
+			} else {
+				$this->parent->splitUntil($parent, $part2, $includeLeft);
+			}
+		}
+		return $splitOccured;
+
+	}
+
+	private function removeChild($index) {
+		unset($this->children[$index]);
+		$this->children = array_values($this->children);
+	}
+
+	public static $blocks = array('html', 'body','p','blockquote', 'h1',
+		'h2', 'h3', 'h4', 'h5', 'pre', 'div', 'ul', 'ol', 'li', 'table',
+		'tbody', 'tr', 'td', 'th', 'br');
+
+	public function copyTree() {
+		$newThis = new TagNode(null, $this->qName, $this->attributes);
+		$newThis->whiteBefore = $this->whiteBefore;
+		$newThis->whiteAfter = $this->whiteAfter;
+		foreach ($this->children as &$child) {
+			$newChild = $child->copyTree();
+			$newChild->setParent($newThis);
+			$newThis->children[] = $newChild;
+		}
+		return $newThis;
+	}
+
+	public function getMatchRatio(TagNode $other) {
+		$txtComp = new TextOnlyComparator($other);
+		return $txtComp->getMatchRatio(new TextOnlyComparator($this));
+	}
+
+	public function expandWhiteSpace() {
+		$shift = 0;
+		$spaceAdded = false;
+
+		$nbOriginalChildren = $this->getNbChildren();
+		for ($i = 0; $i < $nbOriginalChildren; ++$i) {
+			$child = $this->children[$i + $shift];
+
+			if ($child instanceof TagNode) {
+				if (!$child->isPre()) {
+					$child->expandWhiteSpace();
+				}
+			}
+			if (!$spaceAdded && $child->whiteBefore) {
+				$ws = new WhiteSpaceNode(null, ' ', $child->getLeftMostChild());
+				$ws->setParent($this);
+				$this->addChildAbsolute($ws,$i + ($shift++));
+			}
+			if ($child->whiteAfter) {
+				$ws = new WhiteSpaceNode(null, ' ', $child->getRightMostChild());
+				$ws->setParent($this);
+				$this->addChildAbsolute($ws,$i + 1 + ($shift++));
+				$spaceAdded = true;
+			} else {
+				$spaceAdded = false;
+			}
+
+		}
+	}
+
+	public function getLeftMostChild() {
+		if (empty($this->children)) {
+			return $this;
+		}
+		return $this->children[0]->getLeftMostChild();
+	}
+
+	public function getRightMostChild() {
+		if (empty($this->children)) {
+			return $this;
+		}
+		return $this->children[$this->getNbChildren() - 1]->getRightMostChild();
+	}
+
+	public function isPre() {
+		return 0 == strcasecmp($this->qName,'pre');
+	}
+
+	public static function toDiffLine(TagNode $node) {
+		return $node->openingTag;
+	}
+}
+
+/**
+ * Represents a piece of text in the HTML file.
+ * @ingroup DifferenceEngine
+ */
+class TextNode extends Node {
+
+	public $text;
+
+	public $modification;
+
+	function __construct($parent, $text) {
+		parent::__construct($parent);
+		$this->modification = new Modification(Modification::NONE);
+		$this->text = $text;
+	}
+
+	public function copyTree() {
+		$clone = clone $this;
+		$clone->setParent(null);
+		return $clone;
+	}
+
+	public function getLeftMostChild() {
+		return $this;
+	}
+
+	public function getRightMostChild() {
+		return $this;
+	}
+
+	public function getMinimalDeletedSet($id, &$allDeleted, &$somethingDeleted) {
+		if ($this->modification->type == Modification::REMOVED
+					&& $this->modification->id == $id){
+			$somethingDeleted = true;
+			$allDeleted = true;
+			return array($this);
+		}
+		return array();
+	}
+
+	public function isSameText($other) {
+		if (is_null($other) || ! $other instanceof TextNode) {
+			return false;
+		}
+		return str_replace('\n', ' ',$this->text) === str_replace('\n', ' ',$other->text);
+	}
+
+	public static function toDiffLine(TextNode $node) {
+		return str_replace('\n', ' ',$node->text);
+	}
+}
+
+/**
+ * @todo Document
+ * @ingroup DifferenceEngine
+ */
+class WhiteSpaceNode extends TextNode {
+
+	function __construct($parent, $s, Node $like = null) {
+		parent::__construct($parent, $s);
+		if(!is_null($like) && $like instanceof TextNode) {
+			$newModification = clone $like->modification;
+			$newModification->firstOfID = false;
+			$this->modification = $newModification;
+		}
+	}
+}
+
+/**
+ * Represents the root of a HTML document.
+ * @ingroup DifferenceEngine
+ */
+class BodyNode extends TagNode {
+
+	function __construct() {
+		parent::__construct(null, 'body', array());
+	}
+
+	public function copyTree() {
+		$newThis = new BodyNode();
+		foreach ($this->children as &$child) {
+			$newChild = $child->copyTree();
+			$newChild->setParent($newThis);
+			$newThis->children[] = $newChild;
+		}
+		return $newThis;
+	}
+
+	public function getMinimalDeletedSet($id, &$allDeleted, &$somethingDeleted) {
+		$nodes = array();
+		foreach ($this->children as &$child) {
+			$childrenChildren = $child->getMinimalDeletedSet($id,
+						$allDeleted, $somethingDeleted);
+			$nodes = array_merge($nodes, $childrenChildren);
+		}
+		return $nodes;
+	}
+
+}
+
+/**
+ * Represents an image in HTML. Even though images do not contain any text they
+ * are independent visible objects on the page. They are logically a TextNode.
+ * @ingroup DifferenceEngine
+ */
+class ImageNode extends TextNode {
+
+	public $attributes;
+
+	function __construct(TagNode $parent, /*array*/ $attrs) {
+		if(!array_key_exists('src', $attrs)) {
+			HTMLDiffer::diffDebug( "Image without a source\n" );
+			parent::__construct($parent, '<img></img>');
+		}else{
+			parent::__construct($parent, '<img>' . strtolower($attrs['src']) . '</img>');
+		}
+		$this->attributes = $attrs;
+	}
+
+	public function isSameText($other) {
+		if (is_null($other) || ! $other instanceof ImageNode) {
+			return false;
+		}
+		return $this->text === $other->text;
+	}
+
+}
+
+/**
+ * No-op node
+ * @ingroup DifferenceEngine
+ */
+class DummyNode extends Node {
+
+	function __construct() {
+		// no op
+	}
+
+}
-- 
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