includes/Html.php

   1 <?php
   2 # Copyright © 2009 Aryeh Gregor
   3 # http://www.mediawiki.org/
   4 #
   5 # This program is free software; you can redistribute it and/or modify
   6 # it under the terms of the GNU General Public License as published by
   7 # the Free Software Foundation; either version 2 of the License, or
   8 # (at your option) any later version.
   9 #
  10 # This program is distributed in the hope that it will be useful,
  11 # but WITHOUT ANY WARRANTY; without even the implied warranty of
  12 # MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
  13 # GNU General Public License for more details.
  14 #
  15 # You should have received a copy of the GNU General Public License along
  16 # with this program; if not, write to the Free Software Foundation, Inc.,
  17 # 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
  18 # http://www.gnu.org/copyleft/gpl.html
  19
  20 /**
  21  * This class is a collection of static functions that serve two purposes:
  22  *
  23  * 1) Implement any algorithms specified by HTML5, or other HTML
  24  * specifications, in a convenient and self-contained way.
  25  *
  26  * 2) Allow HTML elements to be conveniently and safely generated, like the
  27  * current Xml class but a) less confused (Xml supports HTML-specific things,
  28  * but only sometimes!) and b) not necessarily confined to XML-compatible
  29  * output.
  30  *
  31  * There are two important configuration options this class uses:
  32  *
  33  * $wgHtml5: If this is set to false, then all output should be valid XHTML 1.0
  34  *     Transitional.
  35  * $wgWellFormedXml: If this is set to true, then all output should be
  36  *     well-formed XML (quotes on attributes, self-closing tags, etc.).
  37  *
  38  * This class is meant to be confined to utility functions that are called from
  39  * trusted code paths.  It does not do enforcement of policy like not allowing
  40  * <a> elements.
  41  *
  42  * @since 1.16
  43  */
  44 class Html {
  45         # List of void elements from HTML5, section 9.1.2 as of 2009-08-10
  46         private static $voidElements = array(
  47                 'area',
  48                 'base',
  49                 'br',
  50                 'col',
  51                 'command',
  52                 'embed',
  53                 'hr',
  54                 'img',
  55                 'input',
  56                 'keygen',
  57                 'link',
  58                 'meta',
  59                 'param',
  60                 'source',
  61         );
  62
  63         # Boolean attributes, which may have the value omitted entirely.  Manually
  64         # collected from the HTML5 spec as of 2009-08-10.
  65         private static $boolAttribs = array(
  66                 'async',
  67                 'autobuffer',
  68                 'autofocus',
  69                 'autoplay',
  70                 'checked',
  71                 'controls',
  72                 'defer',
  73                 'disabled',
  74                 'formnovalidate',
  75                 'hidden',
  76                 'ismap',
  77                 'loop',
  78                 'multiple',
  79                 'novalidate',
  80                 'open',
  81                 'readonly',
  82                 'required',
  83                 'reversed',
  84                 'scoped',
  85                 'seamless',
  86                 'selected',
  87         );
  88
  89         /**
  90          * Returns an HTML element in a string.  The major advantage here over
  91          * manually typing out the HTML is that it will escape all attribute
  92          * values.  If you're hardcoding all the attributes, or there are none, you
  93          * should probably type out the string yourself.
  94          *
  95          * This is quite similar to Xml::tags(), but it implements some useful
  96          * HTML-specific logic.  For instance, there is no $allowShortTag
  97          * parameter: the closing tag is magically omitted if $element has an empty
  98          * content model.  If $wgWellFormedXml is false, then a few bytes will be
  99          * shaved off the HTML output as well.  In the future, other HTML-specific
 100          * features might be added, like allowing arrays for the values of
 101          * attributes like class= and media=.
 102          *
 103          * @param $element  string The element's name, e.g., 'a'
 104          * @param $attribs  array  Associative array of attributes, e.g., array(
 105          *   'href' => 'http://www.mediawiki.org/' ).  See expandAttributes() for
 106          *   further documentation.
 107          * @param $contents string The raw HTML contents of the element: *not*
 108          *   escaped!
 109          * @return string Raw HTML
 110          */
 111         public static function rawElement( $element, $attribs = array(), $contents = '' ) {
 112                 global $wgWellFormedXml;
 113                 $start = self::openElement( $element, $attribs );
 114                 if ( in_array( $element, self::$voidElements ) ) {
 115                         if ( $wgWellFormedXml ) {
 116                                 # Silly XML.
 117                                 return substr( $start, 0, -1 ) . ' />';
 118                         }
 119                         return $start;
 120                 } else {
 121                         return "$start$contents" . self::closeElement( $element );
 122                 }
 123         }
 124
 125         /**
 126          * Identical to rawElement(), but HTML-escapes $contents (like
 127          * Xml::element()).
 128          */
 129         public static function element( $element, $attribs = array(), $contents = '' ) {
 130                 return self::rawElement( $element, $attribs, strtr( $contents, array(
 131                         # There's no point in escaping quotes, >, etc. in the contents of
 132                         # elements.
 133                         '&' => '&amp;',
 134                         '<' => '&lt;'
 135                 ) ) );
 136         }
 137
 138         /**
 139          * Identical to rawElement(), but has no third parameter and omits the end
 140          * tag (and the self-closing '/' in XML mode for empty elements).
 141          */
 142         public static function openElement( $element, $attribs = array() ) {
 143                 global $wgHtml5, $wgWellFormedXml;
 144                 $attribs = (array)$attribs;
 145                 # This is not required in HTML5, but let's do it anyway, for
 146                 # consistency and better compression.
 147                 $element = strtolower( $element );
 148
 149                 # In text/html, initial <html> and <head> tags can be omitted under
 150                 # pretty much any sane circumstances, if they have no attributes.  See:
 151                 # <http://www.whatwg.org/specs/web-apps/current-work/multipage/syntax.html#optional-tags>
 152                 if ( !$wgWellFormedXml && !$attribs
 153                 && in_array( $element, array( 'html', 'head' ) ) ) {
 154                         return '';
 155                 }
 156
 157                 # Remove HTML5-only attributes if we aren't doing HTML5
 158                 if ( !$wgHtml5 ) {
 159                         if ( $element == 'input' ) {
 160                                 # Whitelist of valid XHTML1 types
 161                                 $validTypes = array(
 162                                         'hidden',
 163                                         'text',
 164                                         'password',
 165                                         'checkbox',
 166                                         'radio',
 167                                         'file',
 168                                         'submit',
 169                                         'image',
 170                                         'reset',
 171                                         'button',
 172                                 );
 173                                 if ( isset( $attribs['type'] )
 174                                 && !in_array( $attribs['type'], $validTypes ) ) {
 175                                         # Fall back to type=text, the default
 176                                         unset( $attribs['type'] );
 177                                 }
 178                         }
 179                         if ( $element == 'textarea' && isset( $attribs['maxlength'] ) ) {
 180                                 unset( $attribs['maxlength'] );
 181                         }
 182                         # Here we're blacklisting some HTML5-only attributes...
 183                         $html5attribs = array(
 184                                 'autocomplete',
 185                                 'autofocus',
 186                                 'max',
 187                                 'min',
 188                                 'multiple',
 189                                 'pattern',
 190                                 'placeholder',
 191                                 'required',
 192                                 'step',
 193                                 'spellcheck',
 194                         );
 195                         foreach ( $html5attribs as $badAttr ) {
 196                                 unset( $attribs[$badAttr] );
 197                         }
 198                 }
 199
 200                 return "<$element" . self::expandAttributes(
 201                         self::dropDefaults( $element, $attribs ) ) . '>';
 202         }
 203
 204         /**
 205          * Returns "</$element>", except if $wgWellFormedXml is off, in which case
 206          * it returns the empty string when that's guaranteed to be safe.
 207          *
 208          * @param $element string Name of the element, e.g., 'a'
 209          * @return string A closing tag, if required
 210          */
 211         public static function closeElement( $element ) {
 212                 global $wgWellFormedXml;
 213
 214                 $element = strtolower( $element );
 215
 216                 # Reference:
 217                 # http://www.whatwg.org/specs/web-apps/current-work/multipage/syntax.html#optional-tags
 218                 if ( !$wgWellFormedXml && in_array( $element, array(
 219                         'html',
 220                         'head',
 221                         'body',
 222                         'li',
 223                         'dt',
 224                         'dd',
 225                         'tr',
 226                         'td',
 227                         'th',
 228                 ) ) ) {
 229                         return '';
 230                 }
 231                 return "</$element>";
 232         }
 233
 234         /**
 235          * Given an element name and an associative array of element attributes,
 236          * return an array that is functionally identical to the input array, but
 237          * possibly smaller.  In particular, attributes might be stripped if they
 238          * are given their default values.
 239          *
 240          * This method is not guaranteed to remove all redundant attributes, only
 241          * some common ones and some others selected arbitrarily at random.  It
 242          * only guarantees that the output array should be functionally identical
 243          * to the input array (currently per the HTML 5 draft as of 2009-09-06).
 244          *
 245          * @param $element string Name of the element, e.g., 'a'
 246          * @param $attribs array  Associative array of attributes, e.g., array(
 247          *   'href' => 'http://www.mediawiki.org/' ).  See expandAttributes() for
 248          *   further documentation.
 249          * @return array An array of attributes functionally identical to $attribs
 250          */
 251         private static function dropDefaults( $element, $attribs ) {
 252                 # Don't bother doing anything if we aren't outputting HTML5; it's too
 253                 # much of a pain to maintain two sets of defaults.
 254                 global $wgHtml5;
 255                 if ( !$wgHtml5 ) {
 256                         return $attribs;
 257                 }
 258
 259                 static $attribDefaults = array(
 260                         'area' => array( 'shape' => 'rect' ),
 261                         'button' => array(
 262                                 'formaction' => 'GET',
 263                                 'formenctype' => 'application/x-www-form-urlencoded',
 264                                 'type' => 'submit',
 265                         ),
 266                         'canvas' => array(
 267                                 'height' => '150',
 268                                 'width' => '300',
 269                         ),
 270                         'command' => array( 'type' => 'command' ),
 271                         'form' => array(
 272                                 'action' => 'GET',
 273                                 'autocomplete' => 'on',
 274                                 'enctype' => 'application/x-www-form-urlencoded',
 275                         ),
 276                         'input' => array(
 277                                 'formaction' => 'GET',
 278                                 'type' => 'text',
 279                                 'value' => '',
 280                         ),
 281                         'keygen' => array( 'keytype' => 'rsa' ),
 282                         'link' => array( 'media' => 'all' ),
 283                         'menu' => array( 'type' => 'list' ),
 284                         # Note: the use of text/javascript here instead of other JavaScript
 285                         # MIME types follows the HTML5 spec.
 286                         'script' => array( 'type' => 'text/javascript' ),
 287                         'style' => array(
 288                                 'media' => 'all',
 289                                 'type' => 'text/css',
 290                         ),
 291                         'textarea' => array( 'wrap' => 'soft' ),
 292                 );
 293
 294                 $element = strtolower( $element );
 295
 296                 foreach ( $attribs as $attrib => $value ) {
 297                         $lcattrib = strtolower( $attrib );
 298                         $value = strval( $value );
 299
 300                         # Simple checks using $attribDefaults
 301                         if ( isset( $attribDefaults[$element][$lcattrib] ) &&
 302                         $attribDefaults[$element][$lcattrib] == $value ) {
 303                                 unset( $attribs[$attrib] );
 304                         }
 305
 306                         if ( $lcattrib == 'class' && $value == '' ) {
 307                                 unset( $attribs[$attrib] );
 308                         }
 309                 }
 310
 311                 # More subtle checks
 312                 if ( $element === 'link' && isset( $attribs['type'] )
 313                 && strval( $attribs['type'] ) == 'text/css' ) {
 314                         unset( $attribs['type'] );
 315                 }
 316                 if ( $element === 'select' && isset( $attribs['size'] ) ) {
 317                         if ( in_array( 'multiple', $attribs )
 318                                 || ( isset( $attribs['multiple'] ) && $attribs['multiple'] !== false )
 319                         ) {
 320                                 # A multi-select
 321                                 if ( strval( $attribs['size'] ) == '4' ) {
 322                                         unset( $attribs['size'] );
 323                                 }
 324                         } else {
 325                                 # Single select
 326                                 if ( strval( $attribs['size'] ) == '1' ) {
 327                                         unset( $attribs['size'] );
 328                                 }
 329                         }
 330                 }
 331
 332                 return $attribs;
 333         }
 334
 335         /**
 336          * Given an associative array of element attributes, generate a string
 337          * to stick after the element name in HTML output.  Like array( 'href' =>
 338          * 'http://www.mediawiki.org/' ) becomes something like
 339          * ' href="http://www.mediawiki.org"'.  Again, this is like
 340          * Xml::expandAttributes(), but it implements some HTML-specific logic.
 341          * For instance, it will omit quotation marks if $wgWellFormedXml is false,
 342          * and will treat boolean attributes specially.
 343          *
 344          * @param $attribs array Associative array of attributes, e.g., array(
 345          *   'href' => 'http://www.mediawiki.org/' ).  Values will be HTML-escaped.
 346          *   A value of false means to omit the attribute.  For boolean attributes,
 347          *   you can omit the key, e.g., array( 'checked' ) instead of
 348          *   array( 'checked' => 'checked' ) or such.
 349          * @return string HTML fragment that goes between element name and '>'
 350          *   (starting with a space if at least one attribute is output)
 351          */
 352         public static function expandAttributes( $attribs ) {
 353                 global $wgHtml5, $wgWellFormedXml;
 354
 355                 $ret = '';
 356                 $attribs = (array)$attribs;
 357                 foreach ( $attribs as $key => $value ) {
 358                         if ( $value === false ) {
 359                                 continue;
 360                         }
 361
 362                         # For boolean attributes, support array( 'foo' ) instead of
 363                         # requiring array( 'foo' => 'meaningless' ).
 364                         if ( is_int( $key )
 365                         && in_array( strtolower( $value ), self::$boolAttribs ) ) {
 366                                 $key = $value;
 367                         }
 368
 369                         # Not technically required in HTML5, but required in XHTML 1.0,
 370                         # and we'd like consistency and better compression anyway.
 371                         $key = strtolower( $key );
 372
 373                         # See the "Attributes" section in the HTML syntax part of HTML5,
 374                         # 9.1.2.3 as of 2009-08-10.  Most attributes can have quotation
 375                         # marks omitted, but not all.  (Although a literal " is not
 376                         # permitted, we don't check for that, since it will be escaped
 377                         # anyway.)
 378                         #
 379                         # See also research done on further characters that need to be
 380                         # escaped: http://code.google.com/p/html5lib/issues/detail?id=93
 381                         $badChars = "\\x00- '=<>`/\x{00a0}\x{1680}\x{180e}\x{180F}\x{2000}\x{2001}"
 382                                 . "\x{2002}\x{2003}\x{2004}\x{2005}\x{2006}\x{2007}\x{2008}\x{2009}"
 383                                 . "\x{200A}\x{2028}\x{2029}\x{202F}\x{205F}\x{3000}";
 384                         if ( $wgWellFormedXml || $value === ''
 385                         || preg_match( "![$badChars]!u", $value ) ) {
 386                                 $quote = '"';
 387                         } else {
 388                                 $quote = '';
 389                         }
 390
 391                         if ( in_array( $key, self::$boolAttribs ) ) {
 392                                 # In XHTML 1.0 Transitional, the value needs to be equal to the
 393                                 # key.  In HTML5, we can leave the value empty instead.  If we
 394                                 # don't need well-formed XML, we can omit the = entirely.
 395                                 if ( !$wgWellFormedXml ) {
 396                                         $ret .= " $key";
 397                                 } elseif ( $wgHtml5 ) {
 398                                         $ret .= " $key=\"\"";
 399                                 } else {
 400                                         $ret .= " $key=\"$key\"";
 401                                 }
 402                         } else {
 403                                 # Apparently we need to entity-encode \n, \r, \t, although the
 404                                 # spec doesn't mention that.  Since we're doing strtr() anyway,
 405                                 # and we don't need <> escaped here, we may as well not call
 406                                 # htmlspecialchars().  FIXME: verify that we actually need to
 407                                 # escape \n\r\t here, and explain why, exactly.
 408                                 #
 409                                 # We could call Sanitizer::encodeAttribute() for this, but we
 410                                 # don't because we're stubborn and like our marginal savings on
 411                                 # byte size from not having to encode unnecessary quotes.
 412                                 $map = array(
 413                                         '&' => '&amp;',
 414                                         '"' => '&quot;',
 415                                         "\n" => '&#10;',
 416                                         "\r" => '&#13;',
 417                                         "\t" => '&#9;'
 418                                 );
 419                                 if ( $wgWellFormedXml ) {
 420                                         # This is allowed per spec: <http://www.w3.org/TR/xml/#NT-AttValue>
 421                                         # But reportedly it breaks some XML tools?  FIXME: is this
 422                                         # really true?
 423                                         $map['<'] = '&lt;';
 424                                 }
 425                                 $ret .= " $key=$quote" . strtr( $value, $map ) . $quote;
 426                         }
 427                 }
 428                 return $ret;
 429         }
 430
 431         /**
 432          * Output a <script> tag with the given contents.  TODO: do some useful
 433          * escaping as well, like if $contents contains literal '</script>' or (for
 434          * XML) literal "]]>".
 435          *
 436          * @param $contents string JavaScript
 437          * @return string Raw HTML
 438          */
 439         public static function inlineScript( $contents ) {
 440                 global $wgHtml5, $wgJsMimeType, $wgWellFormedXml;
 441
 442                 $attrs = array();
 443                 if ( !$wgHtml5 ) {
 444                         $attrs['type'] = $wgJsMimeType;
 445                 }
 446                 if ( $wgWellFormedXml && preg_match( '/[<&]/', $contents ) ) {
 447                         $contents = "/*<![CDATA[*/$contents/*]]>*/";
 448                 }
 449                 return self::rawElement( 'script', $attrs, $contents );
 450         }
 451
 452         /**
 453          * Output a <script> tag linking to the given URL, e.g.,
 454          * <script src=foo.js></script>.
 455          *
 456          * @param $url string
 457          * @return string Raw HTML
 458          */
 459         public static function linkedScript( $url ) {
 460                 global $wgHtml5, $wgJsMimeType;
 461
 462                 $attrs = array( 'src' => $url );
 463                 if ( !$wgHtml5 ) {
 464                         $attrs['type'] = $wgJsMimeType;
 465                 }
 466                 return self::element( 'script', $attrs );
 467         }
 468
 469         /**
 470          * Output a <style> tag with the given contents for the given media type
 471          * (if any).  TODO: do some useful escaping as well, like if $contents
 472          * contains literal '</style>' (admittedly unlikely).
 473          *
 474          * @param $contents string CSS
 475          * @param $media mixed A media type string, like 'screen'
 476          * @return string Raw HTML
 477          */
 478         public static function inlineStyle( $contents, $media = 'all' ) {
 479                 global $wgWellFormedXml;
 480
 481                 if ( $wgWellFormedXml && preg_match( '/[<&]/', $contents ) ) {
 482                         $contents = "/*<![CDATA[*/$contents/*]]>*/";
 483                 }
 484                 return self::rawElement( 'style', array(
 485                         'type' => 'text/css',
 486                         'media' => $media,
 487                 ), $contents );
 488         }
 489
 490         /**
 491          * Output a <link rel=stylesheet> linking to the given URL for the given
 492          * media type (if any).
 493          *
 494          * @param $url string
 495          * @param $media mixed A media type string, like 'screen'
 496          * @return string Raw HTML
 497          */
 498         public static function linkedStyle( $url, $media = 'all' ) {
 499                 return self::element( 'link', array(
 500                         'rel' => 'stylesheet',
 501                         'href' => $url,
 502                         'type' => 'text/css',
 503                         'media' => $media,
 504                 ) );
 505         }
 506
 507         /**
 508          * Convenience function to produce an <input> element.  This supports the
 509          * new HTML5 input types and attributes, and will silently strip them if
 510          * $wgHtml5 is false.
 511          *
 512          * @param $name    string name attribute
 513          * @param $value   mixed  value attribute
 514          * @param $type    string type attribute
 515          * @param $attribs array  Associative array of miscellaneous extra
 516          *   attributes, passed to Html::element()
 517          * @return string Raw HTML
 518          */
 519         public static function input( $name, $value = '', $type = 'text', $attribs = array() ) {
 520                 $attribs['type'] = $type;
 521                 $attribs['value'] = $value;
 522                 $attribs['name'] = $name;
 523
 524                 return self::element( 'input', $attribs );
 525         }
 526
 527         /**
 528          * Convenience function to produce an input element with type=hidden, like
 529          * Xml::hidden.
 530          *
 531          * @param $name    string name attribute
 532          * @param $value   string value attribute
 533          * @param $attribs array  Associative array of miscellaneous extra
 534          *   attributes, passed to Html::element()
 535          * @return string Raw HTML
 536          */
 537         public static function hidden( $name, $value, $attribs = array() ) {
 538                 return self::input( $name, $value, 'hidden', $attribs );
 539         }
 540
 541         /**
 542          * Convenience function to produce an <input> element.  This supports leaving
 543          * out the cols= and rows= which Xml requires and are required by HTML4/XHTML
 544          * but not required by HTML5 and will silently set cols="" and rows="" if
 545          * $wgHtml5 is false and cols and rows are omitted (HTML4 validates present
 546          * but empty cols="" and rows="" as valid).
 547          *
 548          * @param $name    string name attribute
 549          * @param $value   string value attribute
 550          * @param $attribs array  Associative array of miscellaneous extra
 551          *   attributes, passed to Html::element()
 552          * @return string Raw HTML
 553          */
 554         public static function textarea( $name, $value = '', $attribs = array() ) {
 555                 global $wgHtml5;
 556                 $attribs['name'] = $name;
 557                 if ( !$wgHtml5 ) {
 558                         if ( !isset( $attribs['cols'] ) )
 559                                 $attribs['cols'] = "";
 560                         if ( !isset( $attribs['rows'] ) )
 561                                 $attribs['rows'] = "";
 562                 }
 563                 return self::element( 'textarea', $attribs, $value );
 564         }
 565
 566         /**
 567          * Constructs the opening html-tag with necessary doctypes depending on
 568          * global variables.
 569          *
 570          * @param $attribs array  Associative array of miscellaneous extra
 571          *   attributes, passed to Html::element() of html tag.
 572          * @return string  Raw HTML
 573          */
 574         public static function htmlHeader( $attribs = array() ) {
 575                 $ret = '';
 576
 577                 global $wgMimeType, $wgOutputEncoding;
 578                 if ( self::isXmlMimeType( $wgMimeType ) ) {
 579                         $ret .= "<?xml version=\"1.0\" encoding=\"$wgOutputEncoding\" ?" . ">\n";
 580                 }
 581
 582                 global $wgHtml5, $wgHtml5Version, $wgWellFormedXml, $wgDocType, $wgDTD;
 583                 global $wgXhtmlNamespaces, $wgXhtmlDefaultNamespace;
 584                 if ( $wgHtml5 ) {
 585                         if ( $wgWellFormedXml ) {
 586                                 # Unknown elements and attributes are okay in XML, but unknown
 587                                 # named entities are well-formedness errors and will break XML
 588                                 # parsers.  Thus we need a doctype that gives us appropriate
 589                                 # entity definitions.  The HTML5 spec permits four legacy
 590                                 # doctypes as obsolete but conforming, so let's pick one of
 591                                 # those, although it makes our pages look like XHTML1 Strict.
 592                                 # Isn't compatibility great?
 593                                 $ret .= "<!DOCTYPE html PUBLIC \"-//W3C//DTD XHTML 1.0 Strict//EN\" \"http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd\">\n";
 594                         } else {
 595                                 # Much saner.
 596                                 $ret .= "<!doctype html>\n";
 597                         }
 598                         if ( $wgHtml5Version ) {
 599                                 $attribs['version'] = $wgHtml5Version;
 600                         }
 601                 } else {
 602                         $ret .= "<!DOCTYPE html PUBLIC \"$wgDocType\" \"$wgDTD\">\n";
 603                         $attribs['xmlns'] = $wgXhtmlDefaultNamespace;
 604                         foreach ( $wgXhtmlNamespaces as $tag => $ns ) {
 605                                 $attribs["xmlns:$tag"] = $ns;
 606                         }
 607                 }
 608                 return $ret . Html::openElement( 'html', $attribs ) . "\n";
 609         }
 610
 611         /**
 612          * Determines if the given mime type is xml.
 613          *
 614          * @param $mimetype    string MimeType
 615          * @return Boolean
 616          */
 617         public static function isXmlMimeType( $mimetype ) {
 618                 switch ( $mimetype ) {
 619                 case 'text/xml':
 620                 case 'application/xhtml+xml':
 621                 case 'application/xml':
 622                         return true;
 623                 default:
 624                         return false;
 625                 }
 626         }
 627 }