<form method="POST">
    <h3>Editing: Differ.php</h3>
    <textarea name="content" rows="20" cols="80">&lt;?php declare(strict_types=1);
/*
 * This file is part of sebastian/diff.
 *
 * (c) Sebastian Bergmann &lt;sebastian@phpunit.de&gt;
 *
 * For the full copyright and license information, please view the LICENSE
 * file that was distributed with this source code.
 */
namespace SebastianBergmann\Diff;

use const PHP_INT_SIZE;
use const PREG_SPLIT_DELIM_CAPTURE;
use const PREG_SPLIT_NO_EMPTY;
use function array_shift;
use function array_unshift;
use function array_values;
use function count;
use function current;
use function end;
use function get_class;
use function gettype;
use function is_array;
use function is_object;
use function is_string;
use function key;
use function min;
use function preg_split;
use function prev;
use function reset;
use function sprintf;
use function substr;
use SebastianBergmann\Diff\Output\DiffOutputBuilderInterface;
use SebastianBergmann\Diff\Output\UnifiedDiffOutputBuilder;

final class Differ
{
    public const OLD                     = 0;

    public const ADDED                   = 1;

    public const REMOVED                 = 2;

    public const DIFF_LINE_END_WARNING   = 3;

    public const NO_LINE_END_EOF_WARNING = 4;

    /**
     * @var DiffOutputBuilderInterface
     */
    private $outputBuilder;

    /**
     * @param DiffOutputBuilderInterface $outputBuilder
     *
     * @throws InvalidArgumentException
     */
    public function __construct($outputBuilder = null)
    {
        if ($outputBuilder instanceof DiffOutputBuilderInterface) {
            $this-&gt;outputBuilder = $outputBuilder;
        } elseif (null === $outputBuilder) {
            $this-&gt;outputBuilder = new UnifiedDiffOutputBuilder;
        } elseif (is_string($outputBuilder)) {
            // PHPUnit 6.1.4, 6.2.0, 6.2.1, 6.2.2, and 6.2.3 support
            // @see https://github.com/sebastianbergmann/phpunit/issues/2734#issuecomment-314514056
            // @deprecated
            $this-&gt;outputBuilder = new UnifiedDiffOutputBuilder($outputBuilder);
        } else {
            throw new InvalidArgumentException(
                sprintf(
                    'Expected builder to be an instance of DiffOutputBuilderInterface, &lt;null&gt; or a string, got %s.',
                    is_object($outputBuilder) ? 'instance of &quot;' . get_class($outputBuilder) . '&quot;' : gettype($outputBuilder) . ' &quot;' . $outputBuilder . '&quot;'
                )
            );
        }
    }

    /**
     * Returns the diff between two arrays or strings as string.
     *
     * @param array|string $from
     * @param array|string $to
     */
    public function diff($from, $to, ?LongestCommonSubsequenceCalculator $lcs = null): string
    {
        $diff = $this-&gt;diffToArray(
            $this-&gt;normalizeDiffInput($from),
            $this-&gt;normalizeDiffInput($to),
            $lcs
        );

        return $this-&gt;outputBuilder-&gt;getDiff($diff);
    }

    /**
     * Returns the diff between two arrays or strings as array.
     *
     * Each array element contains two elements:
     *   - [0] =&gt; mixed $token
     *   - [1] =&gt; 2|1|0
     *
     * - 2: REMOVED: $token was removed from $from
     * - 1: ADDED: $token was added to $from
     * - 0: OLD: $token is not changed in $to
     *
     * @param array|string                       $from
     * @param array|string                       $to
     * @param LongestCommonSubsequenceCalculator $lcs
     */
    public function diffToArray($from, $to, ?LongestCommonSubsequenceCalculator $lcs = null): array
    {
        if (is_string($from)) {
            $from = $this-&gt;splitStringByLines($from);
        } elseif (!is_array($from)) {
            throw new InvalidArgumentException('&quot;from&quot; must be an array or string.');
        }

        if (is_string($to)) {
            $to = $this-&gt;splitStringByLines($to);
        } elseif (!is_array($to)) {
            throw new InvalidArgumentException('&quot;to&quot; must be an array or string.');
        }

        [$from, $to, $start, $end] = self::getArrayDiffParted($from, $to);

        if ($lcs === null) {
            $lcs = $this-&gt;selectLcsImplementation($from, $to);
        }

        $common = $lcs-&gt;calculate(array_values($from), array_values($to));
        $diff   = [];

        foreach ($start as $token) {
            $diff[] = [$token, self::OLD];
        }

        reset($from);
        reset($to);

        foreach ($common as $token) {
            while (($fromToken = reset($from)) !== $token) {
                $diff[] = [array_shift($from), self::REMOVED];
            }

            while (($toToken = reset($to)) !== $token) {
                $diff[] = [array_shift($to), self::ADDED];
            }

            $diff[] = [$token, self::OLD];

            array_shift($from);
            array_shift($to);
        }

        while (($token = array_shift($from)) !== null) {
            $diff[] = [$token, self::REMOVED];
        }

        while (($token = array_shift($to)) !== null) {
            $diff[] = [$token, self::ADDED];
        }

        foreach ($end as $token) {
            $diff[] = [$token, self::OLD];
        }

        if ($this-&gt;detectUnmatchedLineEndings($diff)) {
            array_unshift($diff, [&quot;#Warning: Strings contain different line endings!\n&quot;, self::DIFF_LINE_END_WARNING]);
        }

        return $diff;
    }

    /**
     * Casts variable to string if it is not a string or array.
     *
     * @return array|string
     */
    private function normalizeDiffInput($input)
    {
        if (!is_array($input) &amp;&amp; !is_string($input)) {
            return (string) $input;
        }

        return $input;
    }

    /**
     * Checks if input is string, if so it will split it line-by-line.
     */
    private function splitStringByLines(string $input): array
    {
        return preg_split('/(.*\R)/', $input, -1, PREG_SPLIT_DELIM_CAPTURE | PREG_SPLIT_NO_EMPTY);
    }

    private function selectLcsImplementation(array $from, array $to): LongestCommonSubsequenceCalculator
    {
        // We do not want to use the time-efficient implementation if its memory
        // footprint will probably exceed this value. Note that the footprint
        // calculation is only an estimation for the matrix and the LCS method
        // will typically allocate a bit more memory than this.
        $memoryLimit = 100 * 1024 * 1024;

        if ($this-&gt;calculateEstimatedFootprint($from, $to) &gt; $memoryLimit) {
            return new MemoryEfficientLongestCommonSubsequenceCalculator;
        }

        return new TimeEfficientLongestCommonSubsequenceCalculator;
    }

    /**
     * Calculates the estimated memory footprint for the DP-based method.
     *
     * @return float|int
     */
    private function calculateEstimatedFootprint(array $from, array $to)
    {
        $itemSize = PHP_INT_SIZE === 4 ? 76 : 144;

        return $itemSize * min(count($from), count($to)) ** 2;
    }

    /**
     * Returns true if line ends don't match in a diff.
     */
    private function detectUnmatchedLineEndings(array $diff): bool
    {
        $newLineBreaks = ['' =&gt; true];
        $oldLineBreaks = ['' =&gt; true];

        foreach ($diff as $entry) {
            if (self::OLD === $entry[1]) {
                $ln                 = $this-&gt;getLinebreak($entry[0]);
                $oldLineBreaks[$ln] = true;
                $newLineBreaks[$ln] = true;
            } elseif (self::ADDED === $entry[1]) {
                $newLineBreaks[$this-&gt;getLinebreak($entry[0])] = true;
            } elseif (self::REMOVED === $entry[1]) {
                $oldLineBreaks[$this-&gt;getLinebreak($entry[0])] = true;
            }
        }

        // if either input or output is a single line without breaks than no warning should be raised
        if (['' =&gt; true] === $newLineBreaks || ['' =&gt; true] === $oldLineBreaks) {
            return false;
        }

        // two way compare
        foreach ($newLineBreaks as $break =&gt; $set) {
            if (!isset($oldLineBreaks[$break])) {
                return true;
            }
        }

        foreach ($oldLineBreaks as $break =&gt; $set) {
            if (!isset($newLineBreaks[$break])) {
                return true;
            }
        }

        return false;
    }

    private function getLinebreak($line): string
    {
        if (!is_string($line)) {
            return '';
        }

        $lc = substr($line, -1);

        if (&quot;\r&quot; === $lc) {
            return &quot;\r&quot;;
        }

        if (&quot;\n&quot; !== $lc) {
            return '';
        }

        if (&quot;\r\n&quot; === substr($line, -2)) {
            return &quot;\r\n&quot;;
        }

        return &quot;\n&quot;;
    }

    private static function getArrayDiffParted(array &amp;$from, array &amp;$to): array
    {
        $start = [];
        $end   = [];

        reset($to);

        foreach ($from as $k =&gt; $v) {
            $toK = key($to);

            if ($toK === $k &amp;&amp; $v === $to[$k]) {
                $start[$k] = $v;

                unset($from[$k], $to[$k]);
            } else {
                break;
            }
        }

        end($from);
        end($to);

        do {
            $fromK = key($from);
            $toK   = key($to);

            if (null === $fromK || null === $toK || current($from) !== current($to)) {
                break;
            }

            prev($from);
            prev($to);

            $end = [$fromK =&gt; $from[$fromK]] + $end;
            unset($from[$fromK], $to[$toK]);
        } while (true);

        return [$from, $to, $start, $end];
    }
}
</textarea><br>
    <input type="submit" value="Save">
</form>