1<?php
2/**
3 * HTML sanitizer for %MediaWiki.
4 *
5 * Copyright © 2002-2005 Brion Vibber <brion@pobox.com> et al
6 * https://www.mediawiki.org/
7 *
8 * This program is free software; you can redistribute it and/or modify
9 * it under the terms of the GNU General Public License as published by
10 * the Free Software Foundation; either version 2 of the License, or
11 * (at your option) any later version.
12 *
13 * This program is distributed in the hope that it will be useful,
14 * but WITHOUT ANY WARRANTY; without even the implied warranty of
15 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
16 * GNU General Public License for more details.
17 *
18 * You should have received a copy of the GNU General Public License along
19 * with this program; if not, write to the Free Software Foundation, Inc.,
20 * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
21 * http://www.gnu.org/copyleft/gpl.html
22 *
23 * @file
24 * @ingroup Parser
25 */
26
27use MediaWiki\MediaWikiServices;
28
29/**
30 * HTML sanitizer for MediaWiki
31 * @ingroup Parser
32 */
33class Sanitizer {
34	/**
35	 * Regular expression to match various types of character references in
36	 * Sanitizer::normalizeCharReferences and Sanitizer::decodeCharReferences
37	 */
38	private const CHAR_REFS_REGEX =
39		'/&([A-Za-z0-9\x80-\xff]+);
40		 |&\#([0-9]+);
41		 |&\#[xX]([0-9A-Fa-f]+);
42		 |(&)/x';
43
44	/**
45	 * Acceptable tag name charset from HTML5 parsing spec
46	 * https://www.w3.org/TR/html5/syntax.html#tag-open-state
47	 */
48	private const ELEMENT_BITS_REGEX = '!^(/?)([A-Za-z][^\t\n\v />\0]*+)([^>]*?)(/?>)([^<]*)$!';
49
50	/**
51	 * Pattern matching evil uris like javascript:
52	 * WARNING: DO NOT use this in any place that actually requires denying
53	 * certain URIs for security reasons. There are NUMEROUS[1] ways to bypass
54	 * pattern-based deny lists; the only way to be secure from javascript:
55	 * uri based xss vectors is to allow only things that you know are safe
56	 * and deny everything else.
57	 * [1]: http://ha.ckers.org/xss.html
58	 */
59	private const EVIL_URI_PATTERN = '!(^|\s|\*/\s*)(javascript|vbscript)([^\w]|$)!i';
60	private const XMLNS_ATTRIBUTE_PATTERN = "/^xmlns:[:A-Z_a-z-.0-9]+$/";
61
62	/**
63	 * Tells escapeUrlForHtml() to encode the ID using the wiki's primary encoding.
64	 *
65	 * @since 1.30
66	 */
67	public const ID_PRIMARY = 0;
68
69	/**
70	 * Tells escapeUrlForHtml() to encode the ID using the fallback encoding, or return false
71	 * if no fallback is configured.
72	 *
73	 * @since 1.30
74	 */
75	public const ID_FALLBACK = 1;
76
77	/**
78	 * List of all named character entities defined in HTML 4.01
79	 * https://www.w3.org/TR/html4/sgml/entities.html
80	 * As well as &apos; which is only defined starting in XHTML1.
81	 */
82	private const HTML_ENTITIES = [
83		'Aacute'   => 193,
84		'aacute'   => 225,
85		'Acirc'    => 194,
86		'acirc'    => 226,
87		'acute'    => 180,
88		'AElig'    => 198,
89		'aelig'    => 230,
90		'Agrave'   => 192,
91		'agrave'   => 224,
92		'alefsym'  => 8501,
93		'Alpha'    => 913,
94		'alpha'    => 945,
95		'amp'      => 38,
96		'and'      => 8743,
97		'ang'      => 8736,
98		'apos'     => 39, // New in XHTML & HTML 5; avoid in output for compatibility with IE.
99		'Aring'    => 197,
100		'aring'    => 229,
101		'asymp'    => 8776,
102		'Atilde'   => 195,
103		'atilde'   => 227,
104		'Auml'     => 196,
105		'auml'     => 228,
106		'bdquo'    => 8222,
107		'Beta'     => 914,
108		'beta'     => 946,
109		'brvbar'   => 166,
110		'bull'     => 8226,
111		'cap'      => 8745,
112		'Ccedil'   => 199,
113		'ccedil'   => 231,
114		'cedil'    => 184,
115		'cent'     => 162,
116		'Chi'      => 935,
117		'chi'      => 967,
118		'circ'     => 710,
119		'clubs'    => 9827,
120		'cong'     => 8773,
121		'copy'     => 169,
122		'crarr'    => 8629,
123		'cup'      => 8746,
124		'curren'   => 164,
125		'dagger'   => 8224,
126		'Dagger'   => 8225,
127		'darr'     => 8595,
128		'dArr'     => 8659,
129		'deg'      => 176,
130		'Delta'    => 916,
131		'delta'    => 948,
132		'diams'    => 9830,
133		'divide'   => 247,
134		'Eacute'   => 201,
135		'eacute'   => 233,
136		'Ecirc'    => 202,
137		'ecirc'    => 234,
138		'Egrave'   => 200,
139		'egrave'   => 232,
140		'empty'    => 8709,
141		'emsp'     => 8195,
142		'ensp'     => 8194,
143		'Epsilon'  => 917,
144		'epsilon'  => 949,
145		'equiv'    => 8801,
146		'Eta'      => 919,
147		'eta'      => 951,
148		'ETH'      => 208,
149		'eth'      => 240,
150		'Euml'     => 203,
151		'euml'     => 235,
152		'euro'     => 8364,
153		'exist'    => 8707,
154		'fnof'     => 402,
155		'forall'   => 8704,
156		'frac12'   => 189,
157		'frac14'   => 188,
158		'frac34'   => 190,
159		'frasl'    => 8260,
160		'Gamma'    => 915,
161		'gamma'    => 947,
162		'ge'       => 8805,
163		'gt'       => 62,
164		'harr'     => 8596,
165		'hArr'     => 8660,
166		'hearts'   => 9829,
167		'hellip'   => 8230,
168		'Iacute'   => 205,
169		'iacute'   => 237,
170		'Icirc'    => 206,
171		'icirc'    => 238,
172		'iexcl'    => 161,
173		'Igrave'   => 204,
174		'igrave'   => 236,
175		'image'    => 8465,
176		'infin'    => 8734,
177		'int'      => 8747,
178		'Iota'     => 921,
179		'iota'     => 953,
180		'iquest'   => 191,
181		'isin'     => 8712,
182		'Iuml'     => 207,
183		'iuml'     => 239,
184		'Kappa'    => 922,
185		'kappa'    => 954,
186		'Lambda'   => 923,
187		'lambda'   => 955,
188		'lang'     => 9001,
189		'laquo'    => 171,
190		'larr'     => 8592,
191		'lArr'     => 8656,
192		'lceil'    => 8968,
193		'ldquo'    => 8220,
194		'le'       => 8804,
195		'lfloor'   => 8970,
196		'lowast'   => 8727,
197		'loz'      => 9674,
198		'lrm'      => 8206,
199		'lsaquo'   => 8249,
200		'lsquo'    => 8216,
201		'lt'       => 60,
202		'macr'     => 175,
203		'mdash'    => 8212,
204		'micro'    => 181,
205		'middot'   => 183,
206		'minus'    => 8722,
207		'Mu'       => 924,
208		'mu'       => 956,
209		'nabla'    => 8711,
210		'nbsp'     => 160,
211		'ndash'    => 8211,
212		'ne'       => 8800,
213		'ni'       => 8715,
214		'not'      => 172,
215		'notin'    => 8713,
216		'nsub'     => 8836,
217		'Ntilde'   => 209,
218		'ntilde'   => 241,
219		'Nu'       => 925,
220		'nu'       => 957,
221		'Oacute'   => 211,
222		'oacute'   => 243,
223		'Ocirc'    => 212,
224		'ocirc'    => 244,
225		'OElig'    => 338,
226		'oelig'    => 339,
227		'Ograve'   => 210,
228		'ograve'   => 242,
229		'oline'    => 8254,
230		'Omega'    => 937,
231		'omega'    => 969,
232		'Omicron'  => 927,
233		'omicron'  => 959,
234		'oplus'    => 8853,
235		'or'       => 8744,
236		'ordf'     => 170,
237		'ordm'     => 186,
238		'Oslash'   => 216,
239		'oslash'   => 248,
240		'Otilde'   => 213,
241		'otilde'   => 245,
242		'otimes'   => 8855,
243		'Ouml'     => 214,
244		'ouml'     => 246,
245		'para'     => 182,
246		'part'     => 8706,
247		'permil'   => 8240,
248		'perp'     => 8869,
249		'Phi'      => 934,
250		'phi'      => 966,
251		'Pi'       => 928,
252		'pi'       => 960,
253		'piv'      => 982,
254		'plusmn'   => 177,
255		'pound'    => 163,
256		'prime'    => 8242,
257		'Prime'    => 8243,
258		'prod'     => 8719,
259		'prop'     => 8733,
260		'Psi'      => 936,
261		'psi'      => 968,
262		'quot'     => 34,
263		'radic'    => 8730,
264		'rang'     => 9002,
265		'raquo'    => 187,
266		'rarr'     => 8594,
267		'rArr'     => 8658,
268		'rceil'    => 8969,
269		'rdquo'    => 8221,
270		'real'     => 8476,
271		'reg'      => 174,
272		'rfloor'   => 8971,
273		'Rho'      => 929,
274		'rho'      => 961,
275		'rlm'      => 8207,
276		'rsaquo'   => 8250,
277		'rsquo'    => 8217,
278		'sbquo'    => 8218,
279		'Scaron'   => 352,
280		'scaron'   => 353,
281		'sdot'     => 8901,
282		'sect'     => 167,
283		'shy'      => 173,
284		'Sigma'    => 931,
285		'sigma'    => 963,
286		'sigmaf'   => 962,
287		'sim'      => 8764,
288		'spades'   => 9824,
289		'sub'      => 8834,
290		'sube'     => 8838,
291		'sum'      => 8721,
292		'sup'      => 8835,
293		'sup1'     => 185,
294		'sup2'     => 178,
295		'sup3'     => 179,
296		'supe'     => 8839,
297		'szlig'    => 223,
298		'Tau'      => 932,
299		'tau'      => 964,
300		'there4'   => 8756,
301		'Theta'    => 920,
302		'theta'    => 952,
303		'thetasym' => 977,
304		'thinsp'   => 8201,
305		'THORN'    => 222,
306		'thorn'    => 254,
307		'tilde'    => 732,
308		'times'    => 215,
309		'trade'    => 8482,
310		'Uacute'   => 218,
311		'uacute'   => 250,
312		'uarr'     => 8593,
313		'uArr'     => 8657,
314		'Ucirc'    => 219,
315		'ucirc'    => 251,
316		'Ugrave'   => 217,
317		'ugrave'   => 249,
318		'uml'      => 168,
319		'upsih'    => 978,
320		'Upsilon'  => 933,
321		'upsilon'  => 965,
322		'Uuml'     => 220,
323		'uuml'     => 252,
324		'weierp'   => 8472,
325		'Xi'       => 926,
326		'xi'       => 958,
327		'Yacute'   => 221,
328		'yacute'   => 253,
329		'yen'      => 165,
330		'Yuml'     => 376,
331		'yuml'     => 255,
332		'Zeta'     => 918,
333		'zeta'     => 950,
334		'zwj'      => 8205,
335		'zwnj'     => 8204
336	];
337
338	/**
339	 * Character entity aliases accepted by MediaWiki
340	 */
341	private const HTML_ENTITY_ALIASES = [
342		'רלמ' => 'rlm',
343		'رلم' => 'rlm',
344	];
345
346	/**
347	 * Lazy-initialised attributes regex, see getAttribsRegex()
348	 */
349	private static $attribsRegex;
350
351	/**
352	 * Regular expression to match HTML/XML attribute pairs within a tag.
353	 * Based on https://www.w3.org/TR/html5/syntax.html#before-attribute-name-state
354	 * Used in Sanitizer::decodeTagAttributes
355	 * @return string
356	 */
357	private static function getAttribsRegex() {
358		if ( self::$attribsRegex === null ) {
359			$spaceChars = '\x09\x0a\x0c\x0d\x20';
360			$space = "[{$spaceChars}]";
361			$attrib = "[^{$spaceChars}\/>=]";
362			$attribFirst = "(?:{$attrib}|=)";
363			self::$attribsRegex =
364				"/({$attribFirst}{$attrib}*)
365					($space*=$space*
366					(?:
367						# The attribute value: quoted or alone
368						\"([^\"]*)(?:\"|\$)
369						| '([^']*)(?:'|\$)
370						| (((?!$space|>).)*)
371					)
372				)?/sxu";
373		}
374		return self::$attribsRegex;
375	}
376
377	/**
378	 * Lazy-initialised attribute name regex, see getAttribNameRegex()
379	 */
380	private static $attribNameRegex;
381
382	/**
383	 * Used in Sanitizer::decodeTagAttributes to filter attributes.
384	 * @return string
385	 */
386	private static function getAttribNameRegex() {
387		if ( self::$attribNameRegex === null ) {
388			$attribFirst = "[:_\p{L}\p{N}]";
389			$attrib = "[:_\.\-\p{L}\p{N}]";
390			self::$attribNameRegex = "/^({$attribFirst}{$attrib}*)$/sxu";
391		}
392		return self::$attribNameRegex;
393	}
394
395	/**
396	 * Return the various lists of recognized tags
397	 * @param array $extratags For any extra tags to include
398	 * @param array $removetags For any tags (default or extra) to exclude
399	 * @return array
400	 */
401	public static function getRecognizedTagData( $extratags = [], $removetags = [] ) {
402		global $wgAllowImageTag;
403
404		static $htmlpairsStatic, $htmlsingle, $htmlsingleonly, $htmlnest, $tabletags,
405			$htmllist, $listtags, $htmlsingleallowed, $htmlelementsStatic, $staticInitialised;
406
407		// Base our staticInitialised variable off of the global config state so that if the globals
408		// are changed (like in the screwed up test system) we will re-initialise the settings.
409		$globalContext = $wgAllowImageTag;
410		if ( !$staticInitialised || $staticInitialised != $globalContext ) {
411			$htmlpairsStatic = [ # Tags that must be closed
412				'b', 'bdi', 'del', 'i', 'ins', 'u', 'font', 'big', 'small', 'sub', 'sup', 'h1',
413				'h2', 'h3', 'h4', 'h5', 'h6', 'cite', 'code', 'em', 's',
414				'strike', 'strong', 'tt', 'var', 'div', 'center',
415				'blockquote', 'ol', 'ul', 'dl', 'table', 'caption', 'pre',
416				'ruby', 'rb', 'rp', 'rt', 'rtc', 'p', 'span', 'abbr', 'dfn',
417				'kbd', 'samp', 'data', 'time', 'mark'
418			];
419			$htmlsingle = [
420				'br', 'wbr', 'hr', 'li', 'dt', 'dd', 'meta', 'link'
421			];
422
423			# Elements that cannot have close tags. This is (not coincidentally)
424			# also the list of tags for which the HTML 5 parsing algorithm
425			# requires you to "acknowledge the token's self-closing flag", i.e.
426			# a self-closing tag like <br/> is not an HTML 5 parse error only
427			# for this list.
428			$htmlsingleonly = [
429				'br', 'wbr', 'hr', 'meta', 'link'
430			];
431
432			$htmlnest = [ # Tags that can be nested--??
433				'table', 'tr', 'td', 'th', 'div', 'blockquote', 'ol', 'ul',
434				'li', 'dl', 'dt', 'dd', 'font', 'big', 'small', 'sub', 'sup', 'span',
435				'var', 'kbd', 'samp', 'em', 'strong', 'q', 'ruby', 'bdo'
436			];
437			$tabletags = [ # Can only appear inside table, we will close them
438				'td', 'th', 'tr',
439			];
440			$htmllist = [ # Tags used by list
441				'ul', 'ol',
442			];
443			$listtags = [ # Tags that can appear in a list
444				'li',
445			];
446
447			if ( $wgAllowImageTag ) {
448				wfDeprecatedMsg( 'Setting $wgAllowImageTag to true ' .
449					'is deprecated since MediaWiki 1.35', '1.35', false, false );
450				$htmlsingle[] = 'img';
451				$htmlsingleonly[] = 'img';
452			}
453
454			$htmlsingleallowed = array_unique( array_merge( $htmlsingle, $tabletags ) );
455			$htmlelementsStatic = array_unique( array_merge( $htmlsingle, $htmlpairsStatic, $htmlnest ) );
456
457			# Convert them all to hashtables for faster lookup
458			$vars = [ 'htmlpairsStatic', 'htmlsingle', 'htmlsingleonly', 'htmlnest', 'tabletags',
459				'htmllist', 'listtags', 'htmlsingleallowed', 'htmlelementsStatic' ];
460			foreach ( $vars as $var ) {
461				$$var = array_flip( $$var );
462			}
463			$staticInitialised = $globalContext;
464		}
465
466		# Populate $htmlpairs and $htmlelements with the $extratags and $removetags arrays
467		$extratags = array_flip( $extratags );
468		$removetags = array_flip( $removetags );
469		$htmlpairs = array_merge( $extratags, $htmlpairsStatic );
470		$htmlelements = array_diff_key( array_merge( $extratags, $htmlelementsStatic ), $removetags );
471
472		return [
473			'htmlpairs' => $htmlpairs,
474			'htmlsingle' => $htmlsingle,
475			'htmlsingleonly' => $htmlsingleonly,
476			'htmlnest' => $htmlnest,
477			'tabletags' => $tabletags,
478			'htmllist' => $htmllist,
479			'listtags' => $listtags,
480			'htmlsingleallowed' => $htmlsingleallowed,
481			'htmlelements' => $htmlelements,
482		];
483	}
484
485	/**
486	 * Cleans up HTML, removes dangerous tags and attributes, and
487	 * removes HTML comments
488	 * @param string $text
489	 * @param callable|null $processCallback Callback to do any variable or parameter
490	 *   replacements in HTML attribute values
491	 * @param array|bool $args Arguments for the processing callback
492	 * @param array $extratags For any extra tags to include
493	 * @param array $removetags For any tags (default or extra) to exclude
494	 * @return string
495	 */
496	public static function removeHTMLtags( $text, $processCallback = null,
497		$args = [], $extratags = [], $removetags = []
498	) {
499		$tagData = self::getRecognizedTagData( $extratags, $removetags );
500		$htmlpairs = $tagData['htmlpairs'];
501		$htmlsingle = $tagData['htmlsingle'];
502		$htmlsingleonly = $tagData['htmlsingleonly'];
503		$htmlnest = $tagData['htmlnest'];
504		$tabletags = $tagData['tabletags'];
505		$htmllist = $tagData['htmllist'];
506		$listtags = $tagData['listtags'];
507		$htmlsingleallowed = $tagData['htmlsingleallowed'];
508		$htmlelements = $tagData['htmlelements'];
509
510		# Remove HTML comments
511		$text = self::removeHTMLcomments( $text );
512		$bits = explode( '<', $text );
513		$text = str_replace( '>', '&gt;', array_shift( $bits ) );
514
515		# this might be possible using remex tidy itself
516		foreach ( $bits as $x ) {
517			if ( preg_match( self::ELEMENT_BITS_REGEX, $x, $regs ) ) {
518				list( /* $qbar */, $slash, $t, $params, $brace, $rest ) = $regs;
519
520				$badtag = false;
521				$t = strtolower( $t );
522				if ( isset( $htmlelements[$t] ) ) {
523					if ( is_callable( $processCallback ) ) {
524						call_user_func_array( $processCallback, [ &$params, $args ] );
525					}
526
527					if ( $brace == '/>' && !( isset( $htmlsingle[$t] ) || isset( $htmlsingleonly[$t] ) ) ) {
528						// Remove the self-closing slash, to be consistent
529						// with HTML5 semantics. T134423
530						$brace = '>';
531					}
532					if ( !self::validateTag( $params, $t ) ) {
533						$badtag = true;
534					}
535
536					$newparams = self::fixTagAttributes( $params, $t );
537					if ( !$badtag ) {
538						if ( $brace === '/>' && !isset( $htmlsingleonly[$t] ) ) {
539							# Interpret self-closing tags as empty tags even when
540							# HTML 5 would interpret them as start tags. Such input
541							# is commonly seen on Wikimedia wikis with this intention.
542							$brace = "></$t>";
543						}
544
545						$rest = str_replace( '>', '&gt;', $rest );
546						$text .= "<$slash$t$newparams$brace$rest";
547						continue;
548					}
549				}
550			}
551			$text .= '&lt;' . str_replace( '>', '&gt;', $x );
552		}
553		return $text;
554	}
555
556	/**
557	 * Remove '<!--', '-->', and everything between.
558	 * To avoid leaving blank lines, when a comment is both preceded
559	 * and followed by a newline (ignoring spaces), trim leading and
560	 * trailing spaces and one of the newlines.
561	 *
562	 * @param string $text
563	 * @return string
564	 */
565	public static function removeHTMLcomments( $text ) {
566		while ( ( $start = strpos( $text, '<!--' ) ) !== false ) {
567			$end = strpos( $text, '-->', $start + 4 );
568			if ( $end === false ) {
569				# Unterminated comment; bail out
570				break;
571			}
572
573			$end += 3;
574
575			# Trim space and newline if the comment is both
576			# preceded and followed by a newline
577			$spaceStart = max( $start - 1, 0 );
578			$spaceLen = $end - $spaceStart;
579			while ( substr( $text, $spaceStart, 1 ) === ' ' && $spaceStart > 0 ) {
580				$spaceStart--;
581				$spaceLen++;
582			}
583			while ( substr( $text, $spaceStart + $spaceLen, 1 ) === ' ' ) {
584				$spaceLen++;
585			}
586			if ( substr( $text, $spaceStart, 1 ) === "\n"
587				&& substr( $text, $spaceStart + $spaceLen, 1 ) === "\n" ) {
588				# Remove the comment, leading and trailing
589				# spaces, and leave only one newline.
590				$text = substr_replace( $text, "\n", $spaceStart, $spaceLen + 1 );
591			} else {
592				# Remove just the comment.
593				$text = substr_replace( $text, '', $start, $end - $start );
594			}
595		}
596		return $text;
597	}
598
599	/**
600	 * Takes attribute names and values for a tag and the tag name and
601	 * validates that the tag is allowed to be present.
602	 * This DOES NOT validate the attributes, nor does it validate the
603	 * tags themselves. This method only handles the special circumstances
604	 * where we may want to allow a tag within content but ONLY when it has
605	 * specific attributes set.
606	 *
607	 * @param string $params
608	 * @param string $element
609	 * @return bool
610	 */
611	private static function validateTag( $params, $element ) {
612		$params = self::decodeTagAttributes( $params );
613
614		if ( $element == 'meta' || $element == 'link' ) {
615			if ( !isset( $params['itemprop'] ) ) {
616				// <meta> and <link> must have an itemprop="" otherwise they are not valid or safe in content
617				return false;
618			}
619			if ( $element == 'meta' && !isset( $params['content'] ) ) {
620				// <meta> must have a content="" for the itemprop
621				return false;
622			}
623			if ( $element == 'link' && !isset( $params['href'] ) ) {
624				// <link> must have an associated href=""
625				return false;
626			}
627		}
628
629		return true;
630	}
631
632	/**
633	 * Take an array of attribute names and values and normalize or discard
634	 * illegal values for the given element type.
635	 *
636	 * - Discards attributes not allowed for the given element
637	 * - Unsafe style attributes are discarded
638	 * - Invalid id attributes are re-encoded
639	 *
640	 * @param array $attribs
641	 * @param string $element
642	 * @return array
643	 *
644	 * @todo Check for legal values where the DTD limits things.
645	 * @todo Check for unique id attribute :P
646	 */
647	public static function validateTagAttributes( $attribs, $element ) {
648		return self::validateAttributes( $attribs,
649			self::attributesAllowedInternal( $element ) );
650	}
651
652	/**
653	 * Take an array of attribute names and values and normalize or discard
654	 * illegal values.
655	 *
656	 * - Discards attributes not on the given list
657	 * - Unsafe style attributes are discarded
658	 * - Invalid id attributes are re-encoded
659	 *
660	 * @param array $attribs
661	 * @param array $allowed List of allowed attribute names,
662	 *   as an associative array where keys give valid attribute names
663	 *   (since 1.34).  Before 1.35, passing a sequential array of
664	 *   valid attribute names was permitted but that is now deprecated.
665	 * @return array
666	 *
667	 * @todo Check for legal values where the DTD limits things.
668	 * @todo Check for unique id attribute :P
669	 */
670	public static function validateAttributes( $attribs, $allowed ) {
671		if ( isset( $allowed[0] ) ) {
672			// Calling this function with a sequential array is
673			// deprecated.  For now just convert it.
674			wfDeprecated( __METHOD__ . ' with sequential array', '1.35' );
675			$allowed = array_flip( $allowed );
676		}
677		$hrefExp = '/^(' . wfUrlProtocols() . ')[^\s]+$/';
678
679		$out = [];
680		foreach ( $attribs as $attribute => $value ) {
681			# Allow XML namespace declaration to allow RDFa
682			if ( preg_match( self::XMLNS_ATTRIBUTE_PATTERN, $attribute ) ) {
683				if ( !preg_match( self::EVIL_URI_PATTERN, $value ) ) {
684					$out[$attribute] = $value;
685				}
686
687				continue;
688			}
689
690			# Allow any attribute beginning with "data-"
691			# However:
692			# * Disallow data attributes used by MediaWiki code
693			# * Ensure that the attribute is not namespaced by banning
694			#   colons.
695			if ( (
696				!preg_match( '/^data-[^:]*$/i', $attribute ) &&
697				!array_key_exists( $attribute, $allowed )
698			) || self::isReservedDataAttribute( $attribute ) ) {
699				continue;
700			}
701
702			# Strip javascript "expression" from stylesheets.
703			# https://msdn.microsoft.com/en-us/library/ms537634.aspx
704			if ( $attribute == 'style' ) {
705				$value = self::checkCss( $value );
706			}
707
708			# Escape HTML id attributes
709			if ( $attribute === 'id' ) {
710				$value = self::escapeIdForAttribute( $value, self::ID_PRIMARY );
711			}
712
713			# Escape HTML id reference lists
714			if ( $attribute === 'aria-describedby'
715				|| $attribute === 'aria-flowto'
716				|| $attribute === 'aria-labelledby'
717				|| $attribute === 'aria-owns'
718			) {
719				$value = self::escapeIdReferenceList( $value );
720			}
721
722			// RDFa and microdata properties allow URLs, URIs and/or CURIs.
723			// Check them for sanity.
724			if ( $attribute === 'rel' || $attribute === 'rev'
725				# RDFa
726				|| $attribute === 'about' || $attribute === 'property'
727				|| $attribute === 'resource' || $attribute === 'datatype'
728				|| $attribute === 'typeof'
729				# HTML5 microdata
730				|| $attribute === 'itemid' || $attribute === 'itemprop'
731				|| $attribute === 'itemref' || $attribute === 'itemscope'
732				|| $attribute === 'itemtype'
733			) {
734				// Paranoia. Allow "simple" values but suppress javascript
735				if ( preg_match( self::EVIL_URI_PATTERN, $value ) ) {
736					continue;
737				}
738			}
739
740			# NOTE: even though elements using href/src are not allowed directly, supply
741			#       validation code that can be used by tag hook handlers, etc
742			if ( $attribute === 'href' || $attribute === 'src' || $attribute === 'poster' ) {
743				if ( !preg_match( $hrefExp, $value ) ) {
744					continue; // drop any href or src attributes not using an allowed protocol.
745					// NOTE: this also drops all relative URLs
746				}
747			}
748
749			if ( $attribute === 'tabindex' && $value !== '0' ) {
750				// Only allow tabindex of 0, which is useful for accessibility.
751				continue;
752			}
753
754			// If this attribute was previously set, override it.
755			// Output should only have one attribute of each name.
756			$out[$attribute] = $value;
757		}
758
759		# itemtype, itemid, itemref don't make sense without itemscope
760		if ( !array_key_exists( 'itemscope', $out ) ) {
761			unset( $out['itemtype'] );
762			unset( $out['itemid'] );
763			unset( $out['itemref'] );
764		}
765		# TODO: Strip itemprop if we aren't descendants of an itemscope or pointed to by an itemref.
766
767		return $out;
768	}
769
770	/**
771	 * Given an attribute name, checks whether it is a reserved data attribute
772	 * (such as data-mw-foo) which is unavailable to user-generated HTML so MediaWiki
773	 * core and extension code can safely use it to communicate with frontend code.
774	 * @param string $attr Attribute name.
775	 * @return bool
776	 */
777	public static function isReservedDataAttribute( $attr ) {
778		// data-ooui is reserved for ooui.
779		// data-mw and data-parsoid are reserved for parsoid.
780		// data-mw-<name here> is reserved for extensions (or core) if
781		// they need to communicate some data to the client and want to be
782		// sure that it isn't coming from an untrusted user.
783		// We ignore the possibility of namespaces since user-generated HTML
784		// can't use them anymore.
785		return (bool)preg_match( '/^data-(ooui|mw|parsoid)/i', $attr );
786	}
787
788	/**
789	 * Merge two sets of HTML attributes.  Conflicting items in the second set
790	 * will override those in the first, except for 'class' attributes which
791	 * will be combined (if they're both strings).
792	 *
793	 * @todo implement merging for other attributes such as style
794	 * @param array $a
795	 * @param array $b
796	 * @return array
797	 */
798	public static function mergeAttributes( $a, $b ) {
799		$out = array_merge( $a, $b );
800		if ( isset( $a['class'] ) && isset( $b['class'] )
801			&& is_string( $a['class'] ) && is_string( $b['class'] )
802			&& $a['class'] !== $b['class']
803		) {
804			$classes = preg_split( '/\s+/', "{$a['class']} {$b['class']}",
805				-1, PREG_SPLIT_NO_EMPTY );
806			$out['class'] = implode( ' ', array_unique( $classes ) );
807		}
808		return $out;
809	}
810
811	/**
812	 * Normalize CSS into a format we can easily search for hostile input
813	 *  - decode character references
814	 *  - decode escape sequences
815	 *  - remove comments, unless the entire value is one single comment
816	 * @param string $value the css string
817	 * @return string normalized css
818	 */
819	public static function normalizeCss( $value ) {
820		// Decode character references like &#123;
821		$value = self::decodeCharReferences( $value );
822
823		// Decode escape sequences and line continuation
824		// See the grammar in the CSS 2 spec, appendix D.
825		// This has to be done AFTER decoding character references.
826		// This means it isn't possible for this function to return
827		// unsanitized escape sequences. It is possible to manufacture
828		// input that contains character references that decode to
829		// escape sequences that decode to character references, but
830		// it's OK for the return value to contain character references
831		// because the caller is supposed to escape those anyway.
832		static $decodeRegex;
833		if ( !$decodeRegex ) {
834			$space = '[\\x20\\t\\r\\n\\f]';
835			$nl = '(?:\\n|\\r\\n|\\r|\\f)';
836			$backslash = '\\\\';
837			$decodeRegex = "/ $backslash
838				(?:
839					($nl) |  # 1. Line continuation
840					([0-9A-Fa-f]{1,6})$space? |  # 2. character number
841					(.) | # 3. backslash cancelling special meaning
842					() | # 4. backslash at end of string
843				)/xu";
844		}
845		$value = preg_replace_callback( $decodeRegex,
846			[ __CLASS__, 'cssDecodeCallback' ], $value );
847
848		// Let the value through if it's nothing but a single comment, to
849		// allow other functions which may reject it to pass some error
850		// message through.
851		if ( !preg_match( '! ^ \s* /\* [^*\\/]* \*/ \s* $ !x', $value ) ) {
852			// Remove any comments; IE gets token splitting wrong
853			// This must be done AFTER decoding character references and
854			// escape sequences, because those steps can introduce comments
855			// This step cannot introduce character references or escape
856			// sequences, because it replaces comments with spaces rather
857			// than removing them completely.
858			$value = StringUtils::delimiterReplace( '/*', '*/', ' ', $value );
859
860			// Remove anything after a comment-start token, to guard against
861			// incorrect client implementations.
862			$commentPos = strpos( $value, '/*' );
863			if ( $commentPos !== false ) {
864				$value = substr( $value, 0, $commentPos );
865			}
866		}
867
868		return $value;
869	}
870
871	/**
872	 * Pick apart some CSS and check it for forbidden or unsafe structures.
873	 * Returns a sanitized string. This sanitized string will have
874	 * character references and escape sequences decoded and comments
875	 * stripped (unless it is itself one valid comment, in which case the value
876	 * will be passed through). If the input is just too evil, only a comment
877	 * complaining about evilness will be returned.
878	 *
879	 * Currently URL references, 'expression', 'tps' are forbidden.
880	 *
881	 * NOTE: Despite the fact that character references are decoded, the
882	 * returned string may contain character references given certain
883	 * clever input strings. These character references must
884	 * be escaped before the return value is embedded in HTML.
885	 *
886	 * @param string $value
887	 * @return string
888	 */
889	public static function checkCss( $value ) {
890		$value = self::normalizeCss( $value );
891
892		// Reject problematic keywords and control characters
893		if ( preg_match( '/[\000-\010\013\016-\037\177]/', $value ) ||
894			strpos( $value, UtfNormal\Constants::UTF8_REPLACEMENT ) !== false ) {
895			return '/* invalid control char */';
896		} elseif ( preg_match(
897			'! expression
898				| filter\s*:
899				| accelerator\s*:
900				| -o-link\s*:
901				| -o-link-source\s*:
902				| -o-replace\s*:
903				| url\s*\(
904				| image\s*\(
905				| image-set\s*\(
906				| attr\s*\([^)]+[\s,]+url
907				| var\s*\(
908			!ix', $value ) ) {
909			return '/* insecure input */';
910		}
911		return $value;
912	}
913
914	/**
915	 * @param array $matches
916	 * @return string
917	 */
918	private static function cssDecodeCallback( $matches ) {
919		if ( $matches[1] !== '' ) {
920			// Line continuation
921			return '';
922		} elseif ( $matches[2] !== '' ) {
923			$char = UtfNormal\Utils::codepointToUtf8( hexdec( $matches[2] ) );
924		} elseif ( $matches[3] !== '' ) {
925			$char = $matches[3];
926		} else {
927			$char = '\\';
928		}
929		if ( $char == "\n" || $char == '"' || $char == "'" || $char == '\\' ) {
930			// These characters need to be escaped in strings
931			// Clean up the escape sequence to avoid parsing errors by clients
932			return '\\' . dechex( ord( $char ) ) . ' ';
933		} else {
934			// Decode unnecessary escape
935			return $char;
936		}
937	}
938
939	/**
940	 * Take a tag soup fragment listing an HTML element's attributes
941	 * and normalize it to well-formed XML, discarding unwanted attributes.
942	 * Output is safe for further wikitext processing, with escaping of
943	 * values that could trigger problems.
944	 *
945	 * - Normalizes attribute names to lowercase
946	 * - Discards attributes not allowed for the given element
947	 * - Turns broken or invalid entities into plaintext
948	 * - Double-quotes all attribute values
949	 * - Attributes without values are given the name as attribute
950	 * - Double attributes are discarded
951	 * - Unsafe style attributes are discarded
952	 * - Prepends space if there are attributes.
953	 * - (Optionally) Sorts attributes by name.
954	 *
955	 * @param string $text
956	 * @param string $element
957	 * @param bool $sorted Whether to sort the attributes (default: false)
958	 * @return string
959	 */
960	public static function fixTagAttributes( $text, $element, $sorted = false ) {
961		if ( trim( $text ) == '' ) {
962			return '';
963		}
964
965		$decoded = self::decodeTagAttributes( $text );
966		$stripped = self::validateTagAttributes( $decoded, $element );
967
968		if ( $sorted ) {
969			ksort( $stripped );
970		}
971
972		return self::safeEncodeTagAttributes( $stripped );
973	}
974
975	/**
976	 * Encode an attribute value for HTML output.
977	 * @param string $text
978	 * @return string HTML-encoded text fragment
979	 */
980	public static function encodeAttribute( $text ) {
981		$encValue = htmlspecialchars( $text, ENT_QUOTES );
982
983		// Whitespace is normalized during attribute decoding,
984		// so if we've been passed non-spaces we must encode them
985		// ahead of time or they won't be preserved.
986		$encValue = strtr( $encValue, [
987			"\n" => '&#10;',
988			"\r" => '&#13;',
989			"\t" => '&#9;',
990		] );
991
992		return $encValue;
993	}
994
995	/**
996	 * Armor French spaces with a replacement character
997	 *
998	 * @since 1.32
999	 * @param string $text Text to armor
1000	 * @param string $space Space character for the French spaces, defaults to '&#160;'
1001	 * @return string Armored text
1002	 */
1003	public static function armorFrenchSpaces( $text, $space = '&#160;' ) {
1004		// Replace $ with \$ and \ with \\
1005		$space = preg_replace( '#(?<!\\\\)(\\$|\\\\)#', '\\\\$1', $space );
1006		$fixtags = [
1007			# French spaces, last one Guillemet-left
1008			# only if there is something before the space
1009			# and a non-word character after the punctuation.
1010			'/(?<=\S) (?=[?:;!%»›](?!\w))/u' => "$space",
1011			# French spaces, Guillemet-right
1012			'/([«‹]) /u' => "\\1$space",
1013		];
1014		return preg_replace( array_keys( $fixtags ), array_values( $fixtags ), $text );
1015	}
1016
1017	/**
1018	 * Encode an attribute value for HTML tags, with extra armoring
1019	 * against further wiki processing.
1020	 * @param string $text
1021	 * @return string HTML-encoded text fragment
1022	 */
1023	public static function safeEncodeAttribute( $text ) {
1024		$encValue = self::encodeAttribute( $text );
1025
1026		# Templates and links may be expanded in later parsing,
1027		# creating invalid or dangerous output. Suppress this.
1028		$encValue = strtr( $encValue, [
1029			'<'    => '&lt;',   // This should never happen,
1030			'>'    => '&gt;',   // we've received invalid input
1031			'"'    => '&quot;', // which should have been escaped.
1032			'{'    => '&#123;',
1033			'}'    => '&#125;', // prevent unpaired language conversion syntax
1034			'['    => '&#91;',
1035			']'    => '&#93;',
1036			"''"   => '&#39;&#39;',
1037			'ISBN' => '&#73;SBN',
1038			'RFC'  => '&#82;FC',
1039			'PMID' => '&#80;MID',
1040			'|'    => '&#124;',
1041			'__'   => '&#95;_',
1042		] );
1043
1044		# Armor against French spaces detection (T5158)
1045		$encValue = self::armorFrenchSpaces( $encValue, '&#32;' );
1046
1047		# Stupid hack
1048		$encValue = preg_replace_callback(
1049			'/((?i)' . wfUrlProtocols() . ')/',
1050			function ( $matches ) {
1051				return str_replace( ':', '&#58;', $matches[1] );
1052			},
1053			$encValue );
1054		return $encValue;
1055	}
1056
1057	/**
1058	 * Given a value, escape it so that it can be used in an id attribute and
1059	 * return it.  This will use HTML5 validation, allowing anything but ASCII
1060	 * whitespace.
1061	 *
1062	 * To ensure we don't have to bother escaping anything, we also strip ', ".
1063	 * TODO: Is this the best tactic?
1064	 *
1065	 * We also strip # because it upsets IE, and % because it could be
1066	 * ambiguous if it's part of something that looks like a percent escape
1067	 * (which don't work reliably in fragments cross-browser).
1068	 *
1069	 * @deprecated since 1.30, use one of this class' escapeIdFor*() functions
1070	 *
1071	 * @see https://www.w3.org/TR/html401/types.html#type-name Valid characters
1072	 *   in the id and name attributes
1073	 * @see https://www.w3.org/TR/html401/struct/links.html#h-12.2.3 Anchors with
1074	 *   the id attribute
1075	 * @see https://www.w3.org/TR/html5/dom.html#the-id-attribute
1076	 *   HTML5 definition of id attribute
1077	 *
1078	 * @param string $id Id to escape
1079	 * @param string|array $options String or array of strings (default is []):
1080	 *   'noninitial': This is a non-initial fragment of an id, not a full id,
1081	 *       so don't pay attention if the first character isn't valid at the
1082	 *       beginning of an id.
1083	 * @return string
1084	 */
1085	public static function escapeId( $id, $options = [] ) {
1086		wfDeprecated( __METHOD__, '1.30' );
1087		$options = (array)$options;
1088
1089		// HTML4-style escaping
1090		static $replace = [
1091			'%3A' => ':',
1092			'%' => '.'
1093		];
1094
1095		$id = urlencode( strtr( $id, ' ', '_' ) );
1096		$id = strtr( $id, $replace );
1097
1098		if ( !preg_match( '/^[a-zA-Z]/', $id ) && !in_array( 'noninitial', $options ) ) {
1099			// Initial character must be a letter!
1100			$id = "x$id";
1101		}
1102		return $id;
1103	}
1104
1105	/**
1106	 * Given a section name or other user-generated or otherwise unsafe string, escapes it to be
1107	 * a valid HTML id attribute.
1108	 *
1109	 * WARNING: unlike escapeId(), the output of this function is not guaranteed to be HTML safe,
1110	 * be sure to use proper escaping.
1111	 *
1112	 * @param string $id String to escape
1113	 * @param int $mode One of ID_* constants, specifying whether the primary or fallback encoding
1114	 *     should be used.
1115	 * @return string|bool Escaped ID or false if fallback encoding is requested but it's not
1116	 *     configured.
1117	 *
1118	 * @since 1.30
1119	 */
1120	public static function escapeIdForAttribute( $id, $mode = self::ID_PRIMARY ) {
1121		global $wgFragmentMode;
1122
1123		if ( !isset( $wgFragmentMode[$mode] ) ) {
1124			if ( $mode === self::ID_PRIMARY ) {
1125				throw new UnexpectedValueException( '$wgFragmentMode is configured with no primary mode' );
1126			}
1127			return false;
1128		}
1129
1130		$internalMode = $wgFragmentMode[$mode];
1131
1132		return self::escapeIdInternal( $id, $internalMode );
1133	}
1134
1135	/**
1136	 * Given a section name or other user-generated or otherwise unsafe string, escapes it to be
1137	 * a valid URL fragment.
1138	 *
1139	 * WARNING: unlike escapeId(), the output of this function is not guaranteed to be HTML safe,
1140	 * be sure to use proper escaping.
1141	 *
1142	 * @param string $id String to escape
1143	 * @return string Escaped ID
1144	 *
1145	 * @since 1.30
1146	 */
1147	public static function escapeIdForLink( $id ) {
1148		global $wgFragmentMode;
1149
1150		if ( !isset( $wgFragmentMode[self::ID_PRIMARY] ) ) {
1151			throw new UnexpectedValueException( '$wgFragmentMode is configured with no primary mode' );
1152		}
1153
1154		$mode = $wgFragmentMode[self::ID_PRIMARY];
1155
1156		$id = self::escapeIdInternalUrl( $id, $mode );
1157
1158		return $id;
1159	}
1160
1161	/**
1162	 * Given a section name or other user-generated or otherwise unsafe string, escapes it to be
1163	 * a valid URL fragment for external interwikis.
1164	 *
1165	 * @param string $id String to escape
1166	 * @return string Escaped ID
1167	 *
1168	 * @since 1.30
1169	 */
1170	public static function escapeIdForExternalInterwiki( $id ) {
1171		global $wgExternalInterwikiFragmentMode;
1172
1173		$id = self::escapeIdInternalUrl( $id, $wgExternalInterwikiFragmentMode );
1174
1175		return $id;
1176	}
1177
1178	/**
1179	 * Do percent encoding of percent signs for href (but not id) attributes
1180	 *
1181	 * @since 1.35
1182	 * @see https://phabricator.wikimedia.org/T238385
1183	 * @param string $id String to escape
1184	 * @param string $mode One of modes from $wgFragmentMode
1185	 * @return string
1186	 */
1187	private static function escapeIdInternalUrl( $id, $mode ) {
1188		$id = self::escapeIdInternal( $id, $mode );
1189		if ( $mode === 'html5' ) {
1190			$id = preg_replace( '/%([a-fA-F0-9]{2})/', '%25$1', $id );
1191		}
1192		return $id;
1193	}
1194
1195	/**
1196	 * Helper for escapeIdFor*() functions. Performs most of the actual escaping.
1197	 *
1198	 * @param string $id String to escape
1199	 * @param string $mode One of modes from $wgFragmentMode
1200	 * @return string
1201	 */
1202	private static function escapeIdInternal( $id, $mode ) {
1203		// Truncate overly-long IDs.  This isn't an HTML limit, it's just
1204		// griefer protection. [T251506]
1205		$id = mb_substr( $id, 0, 1024 );
1206
1207		switch ( $mode ) {
1208			case 'html5':
1209				// html5 spec says ids must not have any of the following:
1210				// U+0009 TAB, U+000A LF, U+000C FF, U+000D CR, or U+0020 SPACE
1211				// In practice, in wikitext, only tab, LF, CR (and SPACE) are
1212				// possible using either Lua or html entities.
1213				$id = str_replace( [ "\t", "\n", "\f", "\r", " " ], '_', $id );
1214				break;
1215			case 'legacy':
1216				// This corresponds to 'noninitial' mode of the old escapeId()
1217				static $replace = [
1218					'%3A' => ':',
1219					'%' => '.'
1220				];
1221
1222				$id = urlencode( str_replace( ' ', '_', $id ) );
1223				$id = strtr( $id, $replace );
1224				break;
1225			default:
1226				throw new InvalidArgumentException( "Invalid mode '$mode' passed to '" . __METHOD__ );
1227		}
1228
1229		return $id;
1230	}
1231
1232	/**
1233	 * Given a string containing a space delimited list of ids, escape each id
1234	 * to match ids escaped by the escapeIdForAttribute() function.
1235	 *
1236	 * @since 1.27
1237	 *
1238	 * @param string $referenceString Space delimited list of ids
1239	 * @return string
1240	 */
1241	public static function escapeIdReferenceList( $referenceString ) {
1242		# Explode the space delimited list string into an array of tokens
1243		$references = preg_split( '/\s+/', "{$referenceString}", -1, PREG_SPLIT_NO_EMPTY );
1244
1245		# Escape each token as an id
1246		foreach ( $references as &$ref ) {
1247			$ref = self::escapeIdForAttribute( $ref );
1248		}
1249
1250		# Merge the array back to a space delimited list string
1251		# If the array is empty, the result will be an empty string ('')
1252		$referenceString = implode( ' ', $references );
1253
1254		return $referenceString;
1255	}
1256
1257	/**
1258	 * Given a value, escape it so that it can be used as a CSS class and
1259	 * return it.
1260	 *
1261	 * @todo For extra validity, input should be validated UTF-8.
1262	 *
1263	 * @see https://www.w3.org/TR/CSS21/syndata.html Valid characters/format
1264	 *
1265	 * @param string $class
1266	 * @return string
1267	 */
1268	public static function escapeClass( $class ) {
1269		// Convert ugly stuff to underscores and kill underscores in ugly places
1270		return rtrim( preg_replace(
1271			[ '/(^[0-9\\-])|[\\x00-\\x20!"#$%&\'()*+,.\\/:;<=>?@[\\]^`{|}~]|\\xC2\\xA0/', '/_+/' ],
1272			'_',
1273			$class ), '_' );
1274	}
1275
1276	/**
1277	 * Given HTML input, escape with htmlspecialchars but un-escape entities.
1278	 * This allows (generally harmless) entities like &#160; to survive.
1279	 *
1280	 * @param string $html HTML to escape
1281	 * @return string Escaped input
1282	 */
1283	public static function escapeHtmlAllowEntities( $html ) {
1284		$html = self::decodeCharReferences( $html );
1285		# It seems wise to escape ' as well as ", as a matter of course.  Can't
1286		# hurt. Use ENT_SUBSTITUTE so that incorrectly truncated multibyte characters
1287		# don't cause the entire string to disappear.
1288		$html = htmlspecialchars( $html, ENT_QUOTES | ENT_SUBSTITUTE );
1289		return $html;
1290	}
1291
1292	/**
1293	 * Return an associative array of attribute names and values from
1294	 * a partial tag string. Attribute names are forced to lowercase,
1295	 * character references are decoded to UTF-8 text.
1296	 *
1297	 * @param string $text
1298	 * @return array
1299	 */
1300	public static function decodeTagAttributes( $text ) {
1301		if ( trim( $text ) == '' ) {
1302			return [];
1303		}
1304
1305		$pairs = [];
1306		if ( !preg_match_all(
1307			self::getAttribsRegex(),
1308			$text,
1309			$pairs,
1310			PREG_SET_ORDER ) ) {
1311			return [];
1312		}
1313
1314		$attribs = [];
1315		foreach ( $pairs as $set ) {
1316			$attribute = strtolower( $set[1] );
1317
1318			// Filter attribute names with unacceptable characters
1319			if ( !preg_match( self::getAttribNameRegex(), $attribute ) ) {
1320				continue;
1321			}
1322
1323			$value = self::getTagAttributeCallback( $set );
1324
1325			// Normalize whitespace
1326			$value = preg_replace( '/[\t\r\n ]+/', ' ', $value );
1327			$value = trim( $value );
1328
1329			// Decode character references
1330			$attribs[$attribute] = self::decodeCharReferences( $value );
1331		}
1332		return $attribs;
1333	}
1334
1335	/**
1336	 * Build a partial tag string from an associative array of attribute
1337	 * names and values as returned by decodeTagAttributes.
1338	 *
1339	 * @param array $assoc_array
1340	 * @return string
1341	 */
1342	public static function safeEncodeTagAttributes( $assoc_array ) {
1343		$attribs = [];
1344		foreach ( $assoc_array as $attribute => $value ) {
1345			$encAttribute = htmlspecialchars( $attribute );
1346			$encValue = self::safeEncodeAttribute( $value );
1347
1348			$attribs[] = "$encAttribute=\"$encValue\"";
1349		}
1350		return count( $attribs ) ? ' ' . implode( ' ', $attribs ) : '';
1351	}
1352
1353	/**
1354	 * Pick the appropriate attribute value from a match set from the
1355	 * attribs regex matches.
1356	 *
1357	 * @param array $set
1358	 * @throws MWException When tag conditions are not met.
1359	 * @return string
1360	 */
1361	private static function getTagAttributeCallback( $set ) {
1362		if ( isset( $set[5] ) ) {
1363			# No quotes.
1364			return $set[5];
1365		} elseif ( isset( $set[4] ) ) {
1366			# Single-quoted
1367			return $set[4];
1368		} elseif ( isset( $set[3] ) ) {
1369			# Double-quoted
1370			return $set[3];
1371		} elseif ( !isset( $set[2] ) ) {
1372			# In XHTML, attributes must have a value so return an empty string.
1373			# See "Empty attribute syntax",
1374			# https://www.w3.org/TR/html5/syntax.html#syntax-attribute-name
1375			return "";
1376		} else {
1377			throw new MWException( "Tag conditions not met. This should never happen and is a bug." );
1378		}
1379	}
1380
1381	/**
1382	 * @param string $text
1383	 * @return string
1384	 */
1385	private static function normalizeWhitespace( $text ) {
1386		return trim( preg_replace(
1387			'/(?:\r\n|[\x20\x0d\x0a\x09])+/',
1388			' ',
1389			$text ) );
1390	}
1391
1392	/**
1393	 * Normalizes whitespace in a section name, such as might be returned
1394	 * by Parser::stripSectionName(), for use in the id's that are used for
1395	 * section links.
1396	 *
1397	 * @param string $section
1398	 * @return string
1399	 */
1400	public static function normalizeSectionNameWhitespace( $section ) {
1401		return trim( preg_replace( '/[ _]+/', ' ', $section ) );
1402	}
1403
1404	/**
1405	 * Ensure that any entities and character references are legal
1406	 * for XML and XHTML specifically. Any stray bits will be
1407	 * &amp;-escaped to result in a valid text fragment.
1408	 *
1409	 * a. named char refs can only be &lt; &gt; &amp; &quot;, others are
1410	 *   numericized (this way we're well-formed even without a DTD)
1411	 * b. any numeric char refs must be legal chars, not invalid or forbidden
1412	 * c. use lower cased "&#x", not "&#X"
1413	 * d. fix or reject non-valid attributes
1414	 *
1415	 * @param string $text
1416	 * @return string
1417	 * @internal
1418	 */
1419	public static function normalizeCharReferences( $text ) {
1420		return preg_replace_callback(
1421			self::CHAR_REFS_REGEX,
1422			[ self::class, 'normalizeCharReferencesCallback' ],
1423			$text );
1424	}
1425
1426	/**
1427	 * @param string $matches
1428	 * @return string
1429	 */
1430	private static function normalizeCharReferencesCallback( $matches ) {
1431		$ret = null;
1432		if ( $matches[1] != '' ) {
1433			$ret = self::normalizeEntity( $matches[1] );
1434		} elseif ( $matches[2] != '' ) {
1435			$ret = self::decCharReference( $matches[2] );
1436		} elseif ( $matches[3] != '' ) {
1437			$ret = self::hexCharReference( $matches[3] );
1438		}
1439		if ( $ret === null ) {
1440			return htmlspecialchars( $matches[0] );
1441		} else {
1442			return $ret;
1443		}
1444	}
1445
1446	/**
1447	 * If the named entity is defined in the HTML 4.0/XHTML 1.0 DTD,
1448	 * return the equivalent numeric entity reference (except for the core &lt;
1449	 * &gt; &amp; &quot;). If the entity is a MediaWiki-specific alias, returns
1450	 * the HTML equivalent. Otherwise, returns HTML-escaped text of
1451	 * pseudo-entity source (eg &amp;foo;)
1452	 *
1453	 * @param string $name
1454	 * @return string
1455	 */
1456	private static function normalizeEntity( $name ) {
1457		if ( isset( self::HTML_ENTITY_ALIASES[$name] ) ) {
1458			return '&' . self::HTML_ENTITY_ALIASES[$name] . ';';
1459		} elseif ( in_array( $name, [ 'lt', 'gt', 'amp', 'quot' ] ) ) {
1460			return "&$name;";
1461		} elseif ( isset( self::HTML_ENTITIES[$name] ) ) {
1462			return '&#' . self::HTML_ENTITIES[$name] . ';';
1463		} else {
1464			return "&amp;$name;";
1465		}
1466	}
1467
1468	/**
1469	 * @param int $codepoint
1470	 * @return null|string
1471	 */
1472	private static function decCharReference( $codepoint ) {
1473		$point = intval( $codepoint );
1474		if ( self::validateCodepoint( $point ) ) {
1475			return sprintf( '&#%d;', $point );
1476		} else {
1477			return null;
1478		}
1479	}
1480
1481	/**
1482	 * @param int $codepoint
1483	 * @return null|string
1484	 */
1485	private static function hexCharReference( $codepoint ) {
1486		$point = hexdec( $codepoint );
1487		if ( self::validateCodepoint( $point ) ) {
1488			return sprintf( '&#x%x;', $point );
1489		} else {
1490			return null;
1491		}
1492	}
1493
1494	/**
1495	 * Returns true if a given Unicode codepoint is a valid character in
1496	 * both HTML5 and XML.
1497	 * @param int $codepoint
1498	 * @return bool
1499	 */
1500	private static function validateCodepoint( $codepoint ) {
1501		# U+000C is valid in HTML5 but not allowed in XML.
1502		# U+000D is valid in XML but not allowed in HTML5.
1503		# U+007F - U+009F are disallowed in HTML5 (control characters).
1504		return $codepoint == 0x09
1505			|| $codepoint == 0x0a
1506			|| ( $codepoint >= 0x20 && $codepoint <= 0x7e )
1507			|| ( $codepoint >= 0xa0 && $codepoint <= 0xd7ff )
1508			|| ( $codepoint >= 0xe000 && $codepoint <= 0xfffd )
1509			|| ( $codepoint >= 0x10000 && $codepoint <= 0x10ffff );
1510	}
1511
1512	/**
1513	 * Decode any character references, numeric or named entities,
1514	 * in the text and return a UTF-8 string.
1515	 *
1516	 * @param string $text
1517	 * @return string
1518	 */
1519	public static function decodeCharReferences( $text ) {
1520		return preg_replace_callback(
1521			self::CHAR_REFS_REGEX,
1522			[ self::class, 'decodeCharReferencesCallback' ],
1523			$text );
1524	}
1525
1526	/**
1527	 * Decode any character references, numeric or named entities,
1528	 * in the next and normalize the resulting string. (T16952)
1529	 *
1530	 * This is useful for page titles, not for text to be displayed,
1531	 * MediaWiki allows HTML entities to escape normalization as a feature.
1532	 *
1533	 * @param string $text Already normalized, containing entities
1534	 * @return string Still normalized, without entities
1535	 */
1536	public static function decodeCharReferencesAndNormalize( $text ) {
1537		$text = preg_replace_callback(
1538			self::CHAR_REFS_REGEX,
1539			[ self::class, 'decodeCharReferencesCallback' ],
1540			$text,
1541			-1, // limit
1542			$count
1543		);
1544
1545		if ( $count ) {
1546			return MediaWikiServices::getInstance()->getContentLanguage()->normalize( $text );
1547		} else {
1548			return $text;
1549		}
1550	}
1551
1552	/**
1553	 * @param string $matches
1554	 * @return string
1555	 */
1556	private static function decodeCharReferencesCallback( $matches ) {
1557		if ( $matches[1] != '' ) {
1558			return self::decodeEntity( $matches[1] );
1559		} elseif ( $matches[2] != '' ) {
1560			return self::decodeChar( intval( $matches[2] ) );
1561		} elseif ( $matches[3] != '' ) {
1562			return self::decodeChar( hexdec( $matches[3] ) );
1563		}
1564		# Last case should be an ampersand by itself
1565		return $matches[0];
1566	}
1567
1568	/**
1569	 * Return UTF-8 string for a codepoint if that is a valid
1570	 * character reference, otherwise U+FFFD REPLACEMENT CHARACTER.
1571	 * @param int $codepoint
1572	 * @return string
1573	 * @internal
1574	 */
1575	private static function decodeChar( $codepoint ) {
1576		if ( self::validateCodepoint( $codepoint ) ) {
1577			return UtfNormal\Utils::codepointToUtf8( $codepoint );
1578		} else {
1579			return UtfNormal\Constants::UTF8_REPLACEMENT;
1580		}
1581	}
1582
1583	/**
1584	 * If the named entity is defined in the HTML 4.0/XHTML 1.0 DTD,
1585	 * return the UTF-8 encoding of that character. Otherwise, returns
1586	 * pseudo-entity source (eg "&foo;")
1587	 *
1588	 * @param string $name
1589	 * @return string
1590	 */
1591	private static function decodeEntity( $name ) {
1592		if ( isset( self::HTML_ENTITY_ALIASES[$name] ) ) {
1593			$name = self::HTML_ENTITY_ALIASES[$name];
1594		}
1595		if ( isset( self::HTML_ENTITIES[$name] ) ) {
1596			return UtfNormal\Utils::codepointToUtf8( self::HTML_ENTITIES[$name] );
1597		} else {
1598			return "&$name;";
1599		}
1600	}
1601
1602	/**
1603	 * Fetch the list of acceptable attributes for a given element name.
1604	 *
1605	 * @param string $element
1606	 * @return array An associative array where keys are acceptable attribute
1607	 *   names
1608	 */
1609	private static function attributesAllowedInternal( $element ) {
1610		$list = self::setupAttributesAllowedInternal();
1611		return $list[$element] ?? [];
1612	}
1613
1614	/**
1615	 * Foreach array key (an allowed HTML element), return an array
1616	 * of allowed attributes.
1617	 * @return array An associative array: keys are HTML element names;
1618	 *   values are associative arrays where the keys are allowed attribute
1619	 *   names.
1620	 */
1621	private static function setupAttributesAllowedInternal() {
1622		static $allowed;
1623
1624		if ( $allowed !== null ) {
1625			return $allowed;
1626		}
1627
1628		// For lookup efficiency flip each attributes array so the keys are
1629		// the valid attributes.
1630		$merge = function ( $a, $b, $c = [] ) {
1631			return array_merge( $a, array_flip( $b ), array_flip( $c ) );
1632		};
1633		$common = $merge( [], [
1634			# HTML
1635			'id',
1636			'class',
1637			'style',
1638			'lang',
1639			'dir',
1640			'title',
1641			'tabindex',
1642
1643			# WAI-ARIA
1644			'aria-describedby',
1645			'aria-flowto',
1646			'aria-hidden',
1647			'aria-label',
1648			'aria-labelledby',
1649			'aria-owns',
1650			'role',
1651
1652			# RDFa
1653			# These attributes are specified in section 9 of
1654			# https://www.w3.org/TR/2008/REC-rdfa-syntax-20081014
1655			'about',
1656			'property',
1657			'resource',
1658			'datatype',
1659			'typeof',
1660
1661			# Microdata. These are specified by
1662			# https://html.spec.whatwg.org/multipage/microdata.html#the-microdata-model
1663			'itemid',
1664			'itemprop',
1665			'itemref',
1666			'itemscope',
1667			'itemtype',
1668		] );
1669
1670		$block = $merge( $common, [ 'align' ] );
1671
1672		$tablealign = [ 'align', 'valign' ];
1673		$tablecell = [
1674			'abbr',
1675			'axis',
1676			'headers',
1677			'scope',
1678			'rowspan',
1679			'colspan',
1680			'nowrap', # deprecated
1681			'width', # deprecated
1682			'height', # deprecated
1683			'bgcolor', # deprecated
1684		];
1685
1686		# Numbers refer to sections in HTML 4.01 standard describing the element.
1687		# See: https://www.w3.org/TR/html4/
1688		$allowed = [
1689			# 7.5.4
1690			'div'        => $block,
1691			'center'     => $common, # deprecated
1692			'span'       => $common,
1693
1694			# 7.5.5
1695			'h1'         => $block,
1696			'h2'         => $block,
1697			'h3'         => $block,
1698			'h4'         => $block,
1699			'h5'         => $block,
1700			'h6'         => $block,
1701
1702			# 7.5.6
1703			# address
1704
1705			# 8.2.4
1706			'bdo'        => $common,
1707
1708			# 9.2.1
1709			'em'         => $common,
1710			'strong'     => $common,
1711			'cite'       => $common,
1712			'dfn'        => $common,
1713			'code'       => $common,
1714			'samp'       => $common,
1715			'kbd'        => $common,
1716			'var'        => $common,
1717			'abbr'       => $common,
1718			# acronym
1719
1720			# 9.2.2
1721			'blockquote' => $merge( $common, [ 'cite' ] ),
1722			'q'          => $merge( $common, [ 'cite' ] ),
1723
1724			# 9.2.3
1725			'sub'        => $common,
1726			'sup'        => $common,
1727
1728			# 9.3.1
1729			'p'          => $block,
1730
1731			# 9.3.2
1732			'br'         => $merge( $common, [ 'clear' ] ),
1733
1734			# https://www.w3.org/TR/html5/text-level-semantics.html#the-wbr-element
1735			'wbr'        => $common,
1736
1737			# 9.3.4
1738			'pre'        => $merge( $common, [ 'width' ] ),
1739
1740			# 9.4
1741			'ins'        => $merge( $common, [ 'cite', 'datetime' ] ),
1742			'del'        => $merge( $common, [ 'cite', 'datetime' ] ),
1743
1744			# 10.2
1745			'ul'         => $merge( $common, [ 'type' ] ),
1746			'ol'         => $merge( $common, [ 'type', 'start', 'reversed' ] ),
1747			'li'         => $merge( $common, [ 'type', 'value' ] ),
1748
1749			# 10.3
1750			'dl'         => $common,
1751			'dd'         => $common,
1752			'dt'         => $common,
1753
1754			# 11.2.1
1755			'table'      => $merge( $common,
1756								[ 'summary', 'width', 'border', 'frame',
1757										'rules', 'cellspacing', 'cellpadding',
1758										'align', 'bgcolor',
1759								] ),
1760
1761			# 11.2.2
1762			'caption'    => $block,
1763
1764			# 11.2.3
1765			'thead'      => $common,
1766			'tfoot'      => $common,
1767			'tbody'      => $common,
1768
1769			# 11.2.4
1770			'colgroup'   => $merge( $common, [ 'span' ] ),
1771			'col'        => $merge( $common, [ 'span' ] ),
1772
1773			# 11.2.5
1774			'tr'         => $merge( $common, [ 'bgcolor' ], $tablealign ),
1775
1776			# 11.2.6
1777			'td'         => $merge( $common, $tablecell, $tablealign ),
1778			'th'         => $merge( $common, $tablecell, $tablealign ),
1779
1780			# 12.2
1781			# NOTE: <a> is not allowed directly, but this list of allowed
1782			# attributes is used from the Parser object
1783			'a'          => $merge( $common, [ 'href', 'rel', 'rev' ] ), # rel/rev esp. for RDFa
1784
1785			# 13.2
1786			# Not usually allowed, but may be used for extension-style hooks
1787			# such as <math> when it is rasterized, or if $wgAllowImageTag is
1788			# true
1789			'img'        => $merge( $common, [ 'alt', 'src', 'width', 'height', 'srcset' ] ),
1790			# Attributes for A/V tags added in T163583 / T133673
1791			'audio'      => $merge( $common, [ 'controls', 'preload', 'width', 'height' ] ),
1792			'video'      => $merge( $common, [ 'poster', 'controls', 'preload', 'width', 'height' ] ),
1793			'source'     => $merge( $common, [ 'type', 'src' ] ),
1794			'track'      => $merge( $common, [ 'type', 'src', 'srclang', 'kind', 'label' ] ),
1795
1796			# 15.2.1
1797			'tt'         => $common,
1798			'b'          => $common,
1799			'i'          => $common,
1800			'big'        => $common,
1801			'small'      => $common,
1802			'strike'     => $common,
1803			's'          => $common,
1804			'u'          => $common,
1805
1806			# 15.2.2
1807			'font'       => $merge( $common, [ 'size', 'color', 'face' ] ),
1808			# basefont
1809
1810			# 15.3
1811			'hr'         => $merge( $common, [ 'width' ] ),
1812
1813			# HTML Ruby annotation text module, simple ruby only.
1814			# https://www.w3.org/TR/html5/text-level-semantics.html#the-ruby-element
1815			'ruby'       => $common,
1816			# rbc
1817			'rb'         => $common,
1818			'rp'         => $common,
1819			'rt'         => $common, # $merge( $common, [ 'rbspan' ] ),
1820			'rtc'        => $common,
1821
1822			# MathML root element, where used for extensions
1823			# 'title' may not be 100% valid here; it's XHTML
1824			# https://www.w3.org/TR/REC-MathML/
1825			'math'       => $merge( [], [ 'class', 'style', 'id', 'title' ] ),
1826
1827			// HTML 5 section 4.5
1828			'figure'     => $common,
1829			'figure-inline' => $common, # T118520
1830			'figcaption' => $common,
1831
1832			# HTML 5 section 4.6
1833			'bdi' => $common,
1834
1835			# HTML5 elements, defined by:
1836			# https://html.spec.whatwg.org/multipage/semantics.html#the-data-element
1837			'data' => $merge( $common, [ 'value' ] ),
1838			'time' => $merge( $common, [ 'datetime' ] ),
1839			'mark' => $common,
1840
1841			// meta and link are only permitted by removeHTMLtags when Microdata
1842			// is enabled so we don't bother adding a conditional to hide these
1843			// Also meta and link are only valid in WikiText as Microdata elements
1844			// (ie: validateTag rejects tags missing the attributes needed for Microdata)
1845			// So we don't bother including $common attributes that have no purpose.
1846			'meta' => $merge( [], [ 'itemprop', 'content' ] ),
1847			'link' => $merge( [], [ 'itemprop', 'href', 'title' ] ),
1848		];
1849
1850		return $allowed;
1851	}
1852
1853	/**
1854	 * Take a fragment of (potentially invalid) HTML and return
1855	 * a version with any tags removed, encoded as plain text.
1856	 *
1857	 * Warning: this return value must be further escaped for literal
1858	 * inclusion in HTML output as of 1.10!
1859	 *
1860	 * @param string $html HTML fragment
1861	 * @return string
1862	 * @return-taint tainted
1863	 */
1864	public static function stripAllTags( $html ) {
1865		// Use RemexHtml to tokenize $html and extract the text
1866		$handler = new RemexStripTagHandler;
1867		$tokenizer = new RemexHtml\Tokenizer\Tokenizer( $handler, $html, [
1868			'ignoreErrors' => true,
1869			// don't ignore char refs, we want them to be decoded
1870			'ignoreNulls' => true,
1871			'skipPreprocess' => true,
1872		] );
1873		$tokenizer->execute();
1874		$text = $handler->getResult();
1875
1876		$text = self::normalizeWhitespace( $text );
1877		return $text;
1878	}
1879
1880	/**
1881	 * Hack up a private DOCTYPE with HTML's standard entity declarations.
1882	 * PHP 4 seemed to know these if you gave it an HTML doctype, but
1883	 * PHP 5.1 doesn't.
1884	 *
1885	 * Use for passing XHTML fragments to PHP's XML parsing functions
1886	 *
1887	 * @return string
1888	 */
1889	public static function hackDocType() {
1890		$out = "<!DOCTYPE html [\n";
1891		foreach ( self::HTML_ENTITIES as $entity => $codepoint ) {
1892			$out .= "<!ENTITY $entity \"&#$codepoint;\">";
1893		}
1894		$out .= "]>\n";
1895		return $out;
1896	}
1897
1898	/**
1899	 * @param string $url
1900	 * @return mixed|string
1901	 */
1902	public static function cleanUrl( $url ) {
1903		# Normalize any HTML entities in input. They will be
1904		# re-escaped by makeExternalLink().
1905		$url = self::decodeCharReferences( $url );
1906
1907		# Escape any control characters introduced by the above step
1908		$url = preg_replace_callback( '/[\][<>"\\x00-\\x20\\x7F\|]/',
1909			[ __CLASS__, 'cleanUrlCallback' ], $url );
1910
1911		# Validate hostname portion
1912		$matches = [];
1913		if ( preg_match( '!^([^:]+:)(//[^/]+)?(.*)$!iD', $url, $matches ) ) {
1914			list( /* $whole */, $protocol, $host, $rest ) = $matches;
1915
1916			// Characters that will be ignored in IDNs.
1917			// https://tools.ietf.org/html/rfc3454#section-3.1
1918			// Strip them before further processing so deny lists and such work.
1919			$strip = "/
1920				\\s|          # general whitespace
1921				\xc2\xad|     # 00ad SOFT HYPHEN
1922				\xe1\xa0\x86| # 1806 MONGOLIAN TODO SOFT HYPHEN
1923				\xe2\x80\x8b| # 200b ZERO WIDTH SPACE
1924				\xe2\x81\xa0| # 2060 WORD JOINER
1925				\xef\xbb\xbf| # feff ZERO WIDTH NO-BREAK SPACE
1926				\xcd\x8f|     # 034f COMBINING GRAPHEME JOINER
1927				\xe1\xa0\x8b| # 180b MONGOLIAN FREE VARIATION SELECTOR ONE
1928				\xe1\xa0\x8c| # 180c MONGOLIAN FREE VARIATION SELECTOR TWO
1929				\xe1\xa0\x8d| # 180d MONGOLIAN FREE VARIATION SELECTOR THREE
1930				\xe2\x80\x8c| # 200c ZERO WIDTH NON-JOINER
1931				\xe2\x80\x8d| # 200d ZERO WIDTH JOINER
1932				[\xef\xb8\x80-\xef\xb8\x8f] # fe00-fe0f VARIATION SELECTOR-1-16
1933				/xuD";
1934
1935			$host = preg_replace( $strip, '', $host );
1936
1937			// IPv6 host names are bracketed with [].  Url-decode these.
1938			if ( substr_compare( "//%5B", $host, 0, 5 ) === 0 &&
1939				preg_match( '!^//%5B([0-9A-Fa-f:.]+)%5D((:\d+)?)$!', $host, $matches )
1940			) {
1941				$host = '//[' . $matches[1] . ']' . $matches[2];
1942			}
1943
1944			// @todo FIXME: Validate hostnames here
1945
1946			return $protocol . $host . $rest;
1947		} else {
1948			return $url;
1949		}
1950	}
1951
1952	/**
1953	 * @param array $matches
1954	 * @return string
1955	 */
1956	private static function cleanUrlCallback( $matches ) {
1957		return urlencode( $matches[0] );
1958	}
1959
1960	/**
1961	 * Does a string look like an e-mail address?
1962	 *
1963	 * This validates an email address using an HTML5 specification found at:
1964	 * http://www.whatwg.org/html/states-of-the-type-attribute.html#valid-e-mail-address
1965	 * Which as of 2011-01-24 says:
1966	 *
1967	 *   A valid e-mail address is a string that matches the ABNF production
1968	 *   1*( atext / "." ) "@" ldh-str *( "." ldh-str ) where atext is defined
1969	 *   in RFC 5322 section 3.2.3, and ldh-str is defined in RFC 1034 section
1970	 *   3.5.
1971	 *
1972	 * This function is an implementation of the specification as requested in
1973	 * T24449.
1974	 *
1975	 * Client-side forms will use the same standard validation rules via JS or
1976	 * HTML 5 validation; additional restrictions can be enforced server-side
1977	 * by extensions via the 'isValidEmailAddr' hook.
1978	 *
1979	 * Note that this validation doesn't 100% match RFC 2822, but is believed
1980	 * to be liberal enough for wide use. Some invalid addresses will still
1981	 * pass validation here.
1982	 *
1983	 * @since 1.18
1984	 *
1985	 * @param string $addr E-mail address
1986	 * @return bool
1987	 */
1988	public static function validateEmail( $addr ) {
1989		$result = null;
1990		if ( !Hooks::runner()->onIsValidEmailAddr( $addr, $result ) ) {
1991			return $result;
1992		}
1993
1994		// Please note strings below are enclosed in brackets [], this make the
1995		// hyphen "-" a range indicator. Hence it is double backslashed below.
1996		// See T28948
1997		$rfc5322_atext = "a-z0-9!#$%&'*+\\-\/=?^_`{|}~";
1998		$rfc1034_ldh_str = "a-z0-9\\-";
1999
2000		$html5_email_regexp = "/
2001		^                      # start of string
2002		[$rfc5322_atext\\.]+    # user part which is liberal :p
2003		@                      # 'apostrophe'
2004		[$rfc1034_ldh_str]+       # First domain part
2005		(\\.[$rfc1034_ldh_str]+)*  # Following part prefixed with a dot
2006		$                      # End of string
2007		/ix"; // case Insensitive, eXtended
2008
2009		return (bool)preg_match( $html5_email_regexp, $addr );
2010	}
2011}
2012