[^\;\}]*))?' .
			self::URL_REGEX . '(?P[^;]*)[\;]?/';
		$offset = 0;
		while ( preg_match( $pattern, $source, $match, PREG_OFFSET_CAPTURE, $offset ) ) {
			// Skip fully-qualified URLs and data URIs
			$urlScheme = parse_url( $match['file'][0], PHP_URL_SCHEME );
			if ( $urlScheme ) {
				// Move the offset to the end of the match, leaving it alone
				$offset = $match[0][1] + strlen( $match[0][0] );
				continue;
			}
			// URLs with absolute paths like /w/index.php need to be expanded
			// to absolute URLs but otherwise left alone
			if ( $match['file'][0] !== '' && $match['file'][0][0] === '/' ) {
				// Replace the file path with an expanded (possibly protocol-relative) URL
				// ...but only if wfExpandUrl() is even available.
				// This will not be the case if we're running outside of MW
				$lengthIncrease = 0;
				if ( function_exists( 'wfExpandUrl' ) ) {
					$expanded = wfExpandUrl( $match['file'][0], PROTO_RELATIVE );
					$origLength = strlen( $match['file'][0] );
					$lengthIncrease = strlen( $expanded ) - $origLength;
					$source = substr_replace( $source, $expanded,
						$match['file'][1], $origLength
					);
				}
				// Move the offset to the end of the match, leaving it alone
				$offset = $match[0][1] + strlen( $match[0][0] ) + $lengthIncrease;
				continue;
			}

			// Guard against double slashes, because "some/remote/../foo.png"
			// resolves to "some/remote/foo.png" on (some?) clients (bug 27052).
			if ( substr( $remote, -1 ) == '/' ) {
				$remote = substr( $remote, 0, -1 );
			}

			// Shortcuts
			$embed = $match['embed'][0];
			$pre = $match['pre'][0];
			$post = $match['post'][0];
			$query = $match['query'][0];
			$url = "{$remote}/{$match['file'][0]}";
			$file = "{$local}/{$match['file'][0]}";

			$replacement = false;

			if ( $local !== false && file_exists( $file ) ) {
				// Add version parameter as a time-stamp in ISO 8601 format,
				// using Z for the timezone, meaning GMT
				$url .= '?' . gmdate( 'Y-m-d\TH:i:s\Z', round( filemtime( $file ), -2 ) );
				// Embedding requires a bit of extra processing, so let's skip that if we can
				if ( $embedData && $embed && $match['embed'][1] > 0 ) {
					$data = self::encodeImageAsDataURI( $file );
					if ( $data !== false ) {
						// Build 2 CSS properties; one which uses a base64 encoded data URI in place
						// of the @embed comment to try and retain line-number integrity, and the
						// other with a remapped an versioned URL and an Internet Explorer hack
						// making it ignored in all browsers that support data URIs
						$replacement = "{$pre}url({$data}){$post};{$pre}url({$url}){$post}!ie;";
					}
				}
				if ( $replacement === false ) {
					// Assume that all paths are relative to $remote, and make them absolute
					$replacement = "{$embed}{$pre}url({$url}){$post};";
				}
			} elseif ( $local === false ) {
				// Assume that all paths are relative to $remote, and make them absolute
				$replacement = "{$embed}{$pre}url({$url}{$query}){$post};";
			}
			if ( $replacement !== false ) {
				// Perform replacement on the source
				$source = substr_replace(
					$source, $replacement, $match[0][1], strlen( $match[0][0] )
				);
				// Move the offset to the end of the replacement in the source
				$offset = $match[0][1] + strlen( $replacement );
				continue;
			}
			// Move the offset to the end of the match, leaving it alone
			$offset = $match[0][1] + strlen( $match[0][0] );
		}
		return $source;
	}

	/**
	 * Removes whitespace from CSS data
	 *
	 * @param string $css CSS data to minify
	 * @return string Minified CSS data
	 */
	public static function minify( $css ) {
		return trim(
			str_replace(
				array( '; ', ': ', ' {', '{ ', ', ', '} ', ';}' ),
				array( ';', ':', '{', '{', ',', '}', '}' ),
				preg_replace( array( '/\s+/', '/\/\*.*?\*\//s' ), array( ' ', '' ), $css )
			)
		);
	}
}