diff --git a/wiki/inc/DifferenceEngine.php b/wiki/inc/DifferenceEngine.php
new file mode 100644
index 0000000..70877a4
--- /dev/null
+++ b/wiki/inc/DifferenceEngine.php
@@ -0,0 +1,1544 @@
+<?php
+/**
+ * A PHP diff engine for phpwiki. (Taken from phpwiki-1.3.3)
+ *
+ * Additions by Axel Boldt for MediaWiki
+ *
+ * @copyright (C) 2000, 2001 Geoffrey T. Dairiki <dairiki@dairiki.org>
+ * @license  You may copy this code freely under the conditions of the GPL.
+ */
+define('USE_ASSERTS', function_exists('assert'));
+
+class _DiffOp {
+    var $type;
+    var $orig;
+    var $closing;
+
+    /**
+     * @return _DiffOp
+     */
+    function reverse() {
+        trigger_error("pure virtual", E_USER_ERROR);
+    }
+
+    function norig() {
+        return $this->orig ? count($this->orig) : 0;
+    }
+
+    function nclosing() {
+        return $this->closing ? count($this->closing) : 0;
+    }
+}
+
+class _DiffOp_Copy extends _DiffOp {
+    var $type = 'copy';
+
+    function __construct($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);
+    }
+}
+
+class _DiffOp_Delete extends _DiffOp {
+    var $type = 'delete';
+
+    function __construct($lines) {
+        $this->orig = $lines;
+        $this->closing = false;
+    }
+
+    function reverse() {
+        return new _DiffOp_Add($this->orig);
+    }
+}
+
+class _DiffOp_Add extends _DiffOp {
+    var $type = 'add';
+
+    function __construct($lines) {
+        $this->closing = $lines;
+        $this->orig = false;
+    }
+
+    function reverse() {
+        return new _DiffOp_Delete($this->closing);
+    }
+}
+
+class _DiffOp_Change extends _DiffOp {
+    var $type = 'change';
+
+    function __construct($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.
+ *
+ * @author Geoffrey T. Dairiki
+ * @access private
+ */
+class _DiffEngine {
+
+    var $xchanged = array();
+    var $ychanged = array();
+    var $xv = array();
+    var $yv = array();
+    var $xind = array();
+    var $yind = array();
+    var $seq;
+    var $in_seq;
+    var $lcs;
+
+    /**
+     * @param array $from_lines
+     * @param array $to_lines
+     * @return _DiffOp[]
+     */
+    function diff($from_lines, $to_lines) {
+        $n_from = count($from_lines);
+        $n_to = count($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++)
+            $xhash[$from_lines[$xi]] = 1;
+        for ($yi = $skip; $yi < $n_to - $endskip; $yi++) {
+            $line = $to_lines[$yi];
+            if (($this->ychanged[$yi] = empty($xhash[$line])))
+                continue;
+            $yhash[$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($yhash[$line])))
+                continue;
+            $this->xv[] = $line;
+            $this->xind[] = $xi;
+        }
+
+        // Find the LCS.
+        $this->_compareseq(0, count($this->xv), 0, count($this->yv));
+
+        // 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.
+        $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);
+        }
+        return $edits;
+    }
+
+
+    /**
+     * 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.
+     *
+     * @param integer $xoff
+     * @param integer $xlim
+     * @param integer $yoff
+     * @param integer $ylim
+     * @param integer $nchunks
+     *
+     * @return array
+     */
+    function _diag($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];
+                $switch = false;
+                foreach ($matches as $y) {
+                    if ($switch && $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];
+                        $switch = true;
+                    }
+                }
+            }
+        }
+
+        $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.
+     *
+     * @param integer $xoff
+     * @param integer $xlim
+     * @param integer $yoff
+     * @param integer $ylim
+     */
+    function _compareseq($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).
+     *
+     * @param array $lines
+     * @param array $changed
+     * @param array $other_changed
+     */
+    function _shift_boundaries($lines, &$changed, $other_changed) {
+        $i = 0;
+        $j = 0;
+
+        USE_ASSERTS && assert(count($lines) == count($changed));
+        $len = count($lines);
+        $other_len = count($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]);
+            }
+        }
+    }
+}
+
+/**
+ * Class representing a 'diff' between two sequences of strings.
+ */
+class Diff {
+
+    var $edits;
+
+    /**
+     * Constructor.
+     * Computes diff between sequences of strings.
+     *
+     * @param array $from_lines An array of strings.
+     *                          (Typically these are lines from a file.)
+     * @param array $to_lines   An array of strings.
+     */
+    function __construct($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 Diff  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')
+                $lcs += count($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($lines, count($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($lines, count($lines), 0, $edit->closing);
+        }
+        return $lines;
+    }
+
+    /**
+     * Check a Diff for validity.
+     *
+     * This is here only for debugging purposes.
+     *
+     * @param mixed $from_lines
+     * @param mixed $to_lines
+     */
+    function _check($from_lines, $to_lines) {
+        if (serialize($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);
+    }
+}
+
+/**
+ * FIXME: bad name.
+ */
+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 string[] $from_lines         An array of strings.
+     *                                     (Typically these are lines from a file.)
+     *
+     * @param string[] $to_lines           An array of strings.
+     *
+     * @param string[] $mapped_from_lines  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 string[] $mapped_to_lines    This array should
+     *                                     have the same number of elements as $to_lines.
+     */
+    function __construct($from_lines, $to_lines, $mapped_from_lines, $mapped_to_lines) {
+
+        assert(count($from_lines) == count($mapped_from_lines));
+        assert(count($to_lines) == count($mapped_to_lines));
+
+        parent::__construct($mapped_from_lines, $mapped_to_lines);
+
+        $xi = $yi = 0;
+        $ecnt = count($this->edits);
+        for ($i = 0; $i < $ecnt; $i++) {
+            $orig = &$this->edits[$i]->orig;
+            if (is_array($orig)) {
+                $orig = array_slice($from_lines, $xi, count($orig));
+                $xi += count($orig);
+            }
+
+            $closing = &$this->edits[$i]->closing;
+            if (is_array($closing)) {
+                $closing = array_slice($to_lines, $yi, count($closing));
+                $yi += count($closing);
+            }
+        }
+    }
+}
+
+/**
+ * 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.
+ */
+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 $diff A Diff object.
+     * @return string The formatted output.
+     */
+    function format($diff) {
+
+        $xi = $yi = 1;
+        $x0 = $y0 = 0;
+        $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($block)) {
+                    if (count($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, count($context) - $nlead);
+                    $x0 = $xi - count($context);
+                    $y0 = $yi - count($context);
+                    $block = array();
+                    if ($context)
+                        $block[] = new _DiffOp_Copy($context);
+                }
+                $block[] = $edit;
+            }
+
+            if ($edit->orig)
+                $xi += count($edit->orig);
+            if ($edit->closing)
+                $yi += count($edit->closing);
+        }
+
+        if (is_array($block))
+            $this->_block($x0, $xi - $x0, $y0, $yi - $y0, $block);
+
+        return $this->_end_diff();
+    }
+
+    /**
+     * @param int $xbeg
+     * @param int $xlen
+     * @param int $ybeg
+     * @param int $ylen
+     * @param array $edits
+     */
+    function _block($xbeg, $xlen, $ybeg, $ylen, &$edits) {
+        $this->_start_block($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();
+    }
+
+    function _start_diff() {
+        ob_start();
+    }
+
+    function _end_diff() {
+        $val = ob_get_contents();
+        ob_end_clean();
+        return $val;
+    }
+
+    /**
+     * @param int $xbeg
+     * @param int $xlen
+     * @param int $ybeg
+     * @param int $ylen
+     * @return string
+     */
+    function _block_header($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;
+    }
+
+    /**
+     * @param string $header
+     */
+    function _start_block($header) {
+        echo $header;
+    }
+
+    function _end_block() {
+    }
+
+    function _lines($lines, $prefix = ' ') {
+        foreach ($lines as $line)
+            echo "$prefix ".$this->_escape($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);
+    }
+
+    /**
+     * Escape string
+     *
+     * Override this method within other formatters if escaping required.
+     * Base class requires $str to be returned WITHOUT escaping.
+     *
+     * @param $str string Text string to escape
+     * @return string The escaped string.
+     */
+    function _escape($str){
+        return $str;
+    }
+}
+
+/**
+ * Utilityclass for styling HTML formatted diffs
+ *
+ * Depends on global var $DIFF_INLINESTYLES, if true some minimal predefined
+ * inline styles are used. Useful for HTML mails and RSS feeds
+ *
+ * @author Andreas Gohr <andi@splitbrain.org>
+ */
+class HTMLDiff {
+    /**
+     * Holds the style names and basic CSS
+     */
+    static public $styles = array(
+            'diff-addedline'    => 'background-color: #ddffdd;',
+            'diff-deletedline'  => 'background-color: #ffdddd;',
+            'diff-context'      => 'background-color: #f5f5f5;',
+            'diff-mark'         => 'color: #ff0000;',
+        );
+
+    /**
+     * Return a class or style parameter
+     *
+     * @param string $classname
+     *
+     * @return string
+     */
+    static function css($classname){
+        global $DIFF_INLINESTYLES;
+
+        if($DIFF_INLINESTYLES){
+            if(!isset(self::$styles[$classname])) return '';
+            return 'style="'.self::$styles[$classname].'"';
+        }else{
+            return 'class="'.$classname.'"';
+        }
+    }
+}
+
+/**
+ *  Additions by Axel Boldt follow, partly taken from diff.php, phpwiki-1.3.3
+ *
+ */
+
+define('NBSP', "\xC2\xA0");     // utf-8 non-breaking space.
+
+class _HWLDF_WordAccumulator {
+
+    function __construct() {
+        $this->_lines = array();
+        $this->_line = '';
+        $this->_group = '';
+        $this->_tag = '';
+    }
+
+    function _flushGroup($new_tag) {
+        if ($this->_group !== '') {
+            if ($this->_tag == 'mark')
+                $this->_line .= '<strong '.HTMLDiff::css('diff-mark').'>'.$this->_escape($this->_group).'</strong>';
+            elseif ($this->_tag == 'add')
+                $this->_line .= '<span '.HTMLDiff::css('diff-addedline').'>'.$this->_escape($this->_group).'</span>';
+            elseif ($this->_tag == 'del')
+                $this->_line .= '<span '.HTMLDiff::css('diff-deletedline').'><del>'.$this->_escape($this->_group).'</del></span>';
+            else
+                $this->_line .= $this->_escape($this->_group);
+        }
+        $this->_group = '';
+        $this->_tag = $new_tag;
+    }
+
+    /**
+     * @param string $new_tag
+     */
+    function _flushLine($new_tag) {
+        $this->_flushGroup($new_tag);
+        if ($this->_line != '')
+            $this->_lines[] = $this->_line;
+        $this->_line = '';
+    }
+
+    function addWords($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->_group .= NBSP;
+                $this->_flushLine($tag);
+                $word = substr($word, 1);
+            }
+            assert(!strstr($word, "\n"));
+            $this->_group .= $word;
+        }
+    }
+
+    function getLines() {
+        $this->_flushLine('~done');
+        return $this->_lines;
+    }
+
+    function _escape($str){
+        return hsc($str);
+    }
+}
+
+class WordLevelDiff extends MappedDiff {
+
+    function __construct($orig_lines, $closing_lines) {
+        list ($orig_words, $orig_stripped) = $this->_split($orig_lines);
+        list ($closing_words, $closing_stripped) = $this->_split($closing_lines);
+
+        parent::__construct($orig_words, $closing_words, $orig_stripped, $closing_stripped);
+    }
+
+    function _split($lines) {
+        if (!preg_match_all('/ ( [^\S\n]+ | [0-9_A-Za-z\x80-\xff]+ | . ) (?: (?!< \n) [^\S\n])? /xsu',
+             implode("\n", $lines), $m)) {
+            return array(array(''), array(''));
+        }
+        return array($m[0], $m[1]);
+    }
+
+    function orig() {
+        $orig = new _HWLDF_WordAccumulator;
+
+        foreach ($this->edits as $edit) {
+            if ($edit->type == 'copy')
+                $orig->addWords($edit->orig);
+            elseif ($edit->orig)
+                $orig->addWords($edit->orig, 'mark');
+        }
+        return $orig->getLines();
+    }
+
+    function closing() {
+        $closing = new _HWLDF_WordAccumulator;
+
+        foreach ($this->edits as $edit) {
+            if ($edit->type == 'copy')
+                $closing->addWords($edit->closing);
+            elseif ($edit->closing)
+                $closing->addWords($edit->closing, 'mark');
+        }
+        return $closing->getLines();
+    }
+}
+
+class InlineWordLevelDiff extends MappedDiff {
+
+    function __construct($orig_lines, $closing_lines) {
+        list ($orig_words, $orig_stripped) = $this->_split($orig_lines);
+        list ($closing_words, $closing_stripped) = $this->_split($closing_lines);
+
+        parent::__construct($orig_words, $closing_words, $orig_stripped, $closing_stripped);
+    }
+
+    function _split($lines) {
+        if (!preg_match_all('/ ( [^\S\n]+ | [0-9_A-Za-z\x80-\xff]+ | . ) (?: (?!< \n) [^\S\n])? /xsu',
+             implode("\n", $lines), $m)) {
+            return array(array(''), array(''));
+        }
+        return array($m[0], $m[1]);
+    }
+
+    function inline() {
+        $orig = new _HWLDF_WordAccumulator;
+        foreach ($this->edits as $edit) {
+            if ($edit->type == 'copy')
+                $orig->addWords($edit->closing);
+            elseif ($edit->type == 'change'){
+                $orig->addWords($edit->orig, 'del');
+                $orig->addWords($edit->closing, 'add');
+            } elseif ($edit->type == 'delete')
+                $orig->addWords($edit->orig, 'del');
+            elseif ($edit->type == 'add')
+                $orig->addWords($edit->closing, 'add');
+            elseif ($edit->orig)
+                $orig->addWords($edit->orig, 'del');
+        }
+        return $orig->getLines();
+    }
+}
+
+/**
+ * "Unified" diff formatter.
+ *
+ * This class formats the diff in classic "unified diff" format.
+ *
+ * NOTE: output is plain text and unsafe for use in HTML without escaping.
+ */
+class UnifiedDiffFormatter extends DiffFormatter {
+
+    function __construct($context_lines = 4) {
+        $this->leading_context_lines = $context_lines;
+        $this->trailing_context_lines = $context_lines;
+    }
+
+    function _block_header($xbeg, $xlen, $ybeg, $ylen) {
+        if ($xlen != 1)
+            $xbeg .= "," . $xlen;
+        if ($ylen != 1)
+            $ybeg .= "," . $ylen;
+        return "@@ -$xbeg +$ybeg @@\n";
+    }
+
+    function _added($lines) {
+        $this->_lines($lines, "+");
+    }
+    function _deleted($lines) {
+        $this->_lines($lines, "-");
+    }
+    function _changed($orig, $final) {
+        $this->_deleted($orig);
+        $this->_added($final);
+    }
+}
+
+/**
+ *  Wikipedia Table style diff formatter.
+ *
+ */
+class TableDiffFormatter extends DiffFormatter {
+    var $colspan = 2;
+
+    function __construct() {
+        $this->leading_context_lines = 2;
+        $this->trailing_context_lines = 2;
+    }
+
+    /**
+     * @param Diff $diff
+     * @return string
+     */
+    function format($diff) {
+        // Preserve whitespaces by converting some to non-breaking spaces.
+        // Do not convert all of them to allow word-wrap.
+        $val = parent::format($diff);
+        $val = str_replace('  ','&#160; ', $val);
+        $val = preg_replace('/ (?=<)|(?<=[ >]) /', '&#160;', $val);
+        return $val;
+    }
+
+    function _pre($text){
+        $text = htmlspecialchars($text);
+        return $text;
+    }
+
+    function _block_header($xbeg, $xlen, $ybeg, $ylen) {
+        global $lang;
+        $l1 = $lang['line'].' '.$xbeg;
+        $l2 = $lang['line'].' '.$ybeg;
+        $r = '<tr><td '.HTMLDiff::css('diff-blockheader').' colspan="'.$this->colspan.'">'.$l1.":</td>\n".
+             '<td '.HTMLDiff::css('diff-blockheader').' colspan="'.$this->colspan.'">'.$l2.":</td>\n".
+             "</tr>\n";
+        return $r;
+    }
+
+    function _start_block($header) {
+        print($header);
+    }
+
+    function _end_block() {
+    }
+
+    function _lines($lines, $prefix=' ', $color="white") {
+    }
+
+    function addedLine($line,$escaped=false) {
+        if (!$escaped){
+            $line = $this->_escape($line);
+        }
+        return '<td '.HTMLDiff::css('diff-lineheader').'>+</td>'.
+               '<td '.HTMLDiff::css('diff-addedline').'>' .  $line.'</td>';
+    }
+
+    function deletedLine($line,$escaped=false) {
+        if (!$escaped){
+            $line = $this->_escape($line);
+        }
+        return '<td '.HTMLDiff::css('diff-lineheader').'>-</td>'.
+               '<td '.HTMLDiff::css('diff-deletedline').'>' .  $line.'</td>';
+    }
+
+    function emptyLine() {
+        return '<td colspan="'.$this->colspan.'">&#160;</td>';
+    }
+
+    function contextLine($line) {
+        return '<td '.HTMLDiff::css('diff-lineheader').'>&#160;</td>'.
+               '<td '.HTMLDiff::css('diff-context').'>'.$this->_escape($line).'</td>';
+    }
+
+    function _added($lines) {
+        $this->_addedLines($lines,false);
+    }
+
+    function _addedLines($lines,$escaped=false){
+        foreach ($lines as $line) {
+            print('<tr>' . $this->emptyLine() . $this->addedLine($line,$escaped) . "</tr>\n");
+        }
+    }
+
+    function _deleted($lines) {
+        foreach ($lines as $line) {
+            print('<tr>' . $this->deletedLine($line) . $this->emptyLine() . "</tr>\n");
+        }
+    }
+
+    function _context($lines) {
+        foreach ($lines as $line) {
+            print('<tr>' . $this->contextLine($line) .  $this->contextLine($line) . "</tr>\n");
+        }
+    }
+
+    function _changed($orig, $closing) {
+        $diff = new WordLevelDiff($orig, $closing);  // this escapes the diff data
+        $del = $diff->orig();
+        $add = $diff->closing();
+
+        while ($line = array_shift($del)) {
+            $aline = array_shift($add);
+            print('<tr>' . $this->deletedLine($line,true) . $this->addedLine($aline,true) . "</tr>\n");
+        }
+        $this->_addedLines($add,true); # If any leftovers
+    }
+
+    function _escape($str) {
+        return hsc($str);
+    }
+}
+
+/**
+ *  Inline style diff formatter.
+ *
+ */
+class InlineDiffFormatter extends DiffFormatter {
+    var $colspan = 2;
+
+    function __construct() {
+        $this->leading_context_lines = 2;
+        $this->trailing_context_lines = 2;
+    }
+
+    /**
+     * @param Diff $diff
+     * @return string
+     */
+    function format($diff) {
+        // Preserve whitespaces by converting some to non-breaking spaces.
+        // Do not convert all of them to allow word-wrap.
+        $val = parent::format($diff);
+        $val = str_replace('  ','&#160; ', $val);
+        $val = preg_replace('/ (?=<)|(?<=[ >]) /', '&#160;', $val);
+        return $val;
+    }
+
+    function _pre($text){
+        $text = htmlspecialchars($text);
+        return $text;
+    }
+
+    function _block_header($xbeg, $xlen, $ybeg, $ylen) {
+        global $lang;
+        if ($xlen != 1)
+            $xbeg .= "," . $xlen;
+        if ($ylen != 1)
+            $ybeg .= "," . $ylen;
+        $r = '<tr><td colspan="'.$this->colspan.'" '.HTMLDiff::css('diff-blockheader').'>@@ '.$lang['line']." -$xbeg +$ybeg @@";
+        $r .= ' <span '.HTMLDiff::css('diff-deletedline').'><del>'.$lang['deleted'].'</del></span>';
+        $r .= ' <span '.HTMLDiff::css('diff-addedline').'>'.$lang['created'].'</span>';
+        $r .= "</td></tr>\n";
+        return $r;
+    }
+
+    function _start_block($header) {
+        print($header."\n");
+    }
+
+    function _end_block() {
+    }
+
+    function _lines($lines, $prefix=' ', $color="white") {
+    }
+
+    function _added($lines) {
+        foreach ($lines as $line) {
+            print('<tr><td '.HTMLDiff::css('diff-lineheader').'>&#160;</td><td '.HTMLDiff::css('diff-addedline').'>'. $this->_escape($line) . "</td></tr>\n");
+        }
+    }
+
+    function _deleted($lines) {
+        foreach ($lines as $line) {
+            print('<tr><td '.HTMLDiff::css('diff-lineheader').'>&#160;</td><td '.HTMLDiff::css('diff-deletedline').'><del>' . $this->_escape($line) . "</del></td></tr>\n");
+        }
+    }
+
+    function _context($lines) {
+        foreach ($lines as $line) {
+            print('<tr><td '.HTMLDiff::css('diff-lineheader').'>&#160;</td><td '.HTMLDiff::css('diff-context').'>'. $this->_escape($line) ."</td></tr>\n");
+        }
+    }
+
+    function _changed($orig, $closing) {
+        $diff = new InlineWordLevelDiff($orig, $closing);  // this escapes the diff data
+        $add = $diff->inline();
+
+        foreach ($add as $line)
+            print('<tr><td '.HTMLDiff::css('diff-lineheader').'>&#160;</td><td>'.$line."</td></tr>\n");
+    }
+
+    function _escape($str) {
+        return hsc($str);
+    }
+}
+
+/**
+ * A class for computing three way diffs.
+ *
+ * @author  Geoffrey T. Dairiki <dairiki@dairiki.org>
+ */
+class Diff3 extends Diff {
+
+    /**
+     * Conflict counter.
+     *
+     * @var integer
+     */
+    var $_conflictingBlocks = 0;
+
+    /**
+     * Computes diff between 3 sequences of strings.
+     *
+     * @param array $orig    The original lines to use.
+     * @param array $final1  The first version to compare to.
+     * @param array $final2  The second version to compare to.
+     */
+    function __construct($orig, $final1, $final2) {
+        $engine = new _DiffEngine();
+
+        $this->_edits = $this->_diff3($engine->diff($orig, $final1),
+                                      $engine->diff($orig, $final2));
+    }
+
+    /**
+     * Returns the merged lines
+     *
+     * @param string $label1  label for first version
+     * @param string $label2  label for second version
+     * @param string $label3  separator between versions
+     * @return array          lines of the merged text
+     */
+    function mergedOutput($label1='<<<<<<<',$label2='>>>>>>>',$label3='=======') {
+        $lines = array();
+        foreach ($this->_edits as $edit) {
+            if ($edit->isConflict()) {
+                /* FIXME: this should probably be moved somewhere else. */
+                $lines = array_merge($lines,
+                                     array($label1),
+                                     $edit->final1,
+                                     array($label3),
+                                     $edit->final2,
+                                     array($label2));
+                $this->_conflictingBlocks++;
+            } else {
+                $lines = array_merge($lines, $edit->merged());
+            }
+        }
+
+        return $lines;
+    }
+
+    /**
+     * @access private
+     *
+     * @param array $edits1
+     * @param array $edits2
+     *
+     * @return array
+     */
+    function _diff3($edits1, $edits2) {
+        $edits = array();
+        $bb = new _Diff3_BlockBuilder();
+
+        $e1 = current($edits1);
+        $e2 = current($edits2);
+        while ($e1 || $e2) {
+            if ($e1 && $e2 && is_a($e1, '_DiffOp_copy') && is_a($e2, '_DiffOp_copy')) {
+                /* We have copy blocks from both diffs. This is the (only)
+                 * time we want to emit a diff3 copy block.  Flush current
+                 * diff3 diff block, if any. */
+                if ($edit = $bb->finish()) {
+                    $edits[] = $edit;
+                }
+
+                $ncopy = min($e1->norig(), $e2->norig());
+                assert($ncopy > 0);
+                $edits[] = new _Diff3_Op_copy(array_slice($e1->orig, 0, $ncopy));
+
+                if ($e1->norig() > $ncopy) {
+                    array_splice($e1->orig, 0, $ncopy);
+                    array_splice($e1->closing, 0, $ncopy);
+                } else {
+                    $e1 = next($edits1);
+                }
+
+                if ($e2->norig() > $ncopy) {
+                    array_splice($e2->orig, 0, $ncopy);
+                    array_splice($e2->closing, 0, $ncopy);
+                } else {
+                    $e2 = next($edits2);
+                }
+            } else {
+                if ($e1 && $e2) {
+                    if ($e1->orig && $e2->orig) {
+                        $norig = min($e1->norig(), $e2->norig());
+                        $orig = array_splice($e1->orig, 0, $norig);
+                        array_splice($e2->orig, 0, $norig);
+                        $bb->input($orig);
+                    }
+
+                    if (is_a($e1, '_DiffOp_copy')) {
+                        $bb->out1(array_splice($e1->closing, 0, $norig));
+                    }
+
+                    if (is_a($e2, '_DiffOp_copy')) {
+                        $bb->out2(array_splice($e2->closing, 0, $norig));
+                    }
+                }
+
+                if ($e1 && ! $e1->orig) {
+                    $bb->out1($e1->closing);
+                    $e1 = next($edits1);
+                }
+                if ($e2 && ! $e2->orig) {
+                    $bb->out2($e2->closing);
+                    $e2 = next($edits2);
+                }
+            }
+        }
+
+        if ($edit = $bb->finish()) {
+            $edits[] = $edit;
+        }
+
+        return $edits;
+    }
+}
+
+/**
+ * @author  Geoffrey T. Dairiki <dairiki@dairiki.org>
+ *
+ * @access private
+ */
+class _Diff3_Op {
+
+    function __construct($orig = false, $final1 = false, $final2 = false) {
+        $this->orig = $orig ? $orig : array();
+        $this->final1 = $final1 ? $final1 : array();
+        $this->final2 = $final2 ? $final2 : array();
+    }
+
+    function merged() {
+        if (!isset($this->_merged)) {
+            if ($this->final1 === $this->final2) {
+                $this->_merged = &$this->final1;
+            } elseif ($this->final1 === $this->orig) {
+                $this->_merged = &$this->final2;
+            } elseif ($this->final2 === $this->orig) {
+                $this->_merged = &$this->final1;
+            } else {
+                $this->_merged = false;
+            }
+        }
+
+        return $this->_merged;
+    }
+
+    function isConflict() {
+        return $this->merged() === false;
+    }
+
+}
+
+/**
+ * @author  Geoffrey T. Dairiki <dairiki@dairiki.org>
+ *
+ * @access private
+ */
+class _Diff3_Op_copy extends _Diff3_Op {
+
+    function __construct($lines = false) {
+        $this->orig = $lines ? $lines : array();
+        $this->final1 = &$this->orig;
+        $this->final2 = &$this->orig;
+    }
+
+    function merged() {
+        return $this->orig;
+    }
+
+    function isConflict() {
+        return false;
+    }
+}
+
+/**
+ * @author  Geoffrey T. Dairiki <dairiki@dairiki.org>
+ *
+ * @access private
+ */
+class _Diff3_BlockBuilder {
+
+    function __construct() {
+        $this->_init();
+    }
+
+    function input($lines) {
+        if ($lines) {
+            $this->_append($this->orig, $lines);
+        }
+    }
+
+    function out1($lines) {
+        if ($lines) {
+            $this->_append($this->final1, $lines);
+        }
+    }
+
+    function out2($lines) {
+        if ($lines) {
+            $this->_append($this->final2, $lines);
+        }
+    }
+
+    function isEmpty() {
+        return !$this->orig && !$this->final1 && !$this->final2;
+    }
+
+    function finish() {
+        if ($this->isEmpty()) {
+            return false;
+        } else {
+            $edit = new _Diff3_Op($this->orig, $this->final1, $this->final2);
+            $this->_init();
+            return $edit;
+        }
+    }
+
+    function _init() {
+        $this->orig = $this->final1 = $this->final2 = array();
+    }
+
+    function _append(&$array, $lines) {
+        array_splice($array, sizeof($array), 0, $lines);
+    }
+}
+
+//Setup VIM: ex: et ts=4 :