elements. * * @since 1.16 */ class Html { // List of void elements from HTML5, section 8.1.2 as of 2011-08-12 private static $voidElements = array( 'area', 'base', 'br', 'col', 'command', 'embed', 'hr', 'img', 'input', 'keygen', 'link', 'meta', 'param', 'source', 'track', 'wbr', ); // Boolean attributes, which may have the value omitted entirely. Manually // collected from the HTML5 spec as of 2011-08-12. private static $boolAttribs = array( 'async', 'autofocus', 'autoplay', 'checked', 'controls', 'default', 'defer', 'disabled', 'formnovalidate', 'hidden', 'ismap', 'itemscope', 'loop', 'multiple', 'muted', 'novalidate', 'open', 'pubdate', 'readonly', 'required', 'reversed', 'scoped', 'seamless', 'selected', 'truespeed', 'typemustmatch', // HTML5 Microdata 'itemscope', ); /** * Modifies a set of attributes meant for text input elements * and apply a set of default attributes. * Removes size attribute when $wgUseMediaWikiUIEverywhere enabled. * @param array $attrs An attribute array. * @return array $attrs A modified attribute array */ public static function getTextInputAttributes( $attrs ) { global $wgUseMediaWikiUIEverywhere; if ( !$attrs ) { $attrs = array(); } if ( isset( $attrs['class'] ) ) { if ( is_array( $attrs['class'] ) ) { $attrs['class'][] = 'mw-ui-input'; } else { $attrs['class'] .= ' mw-ui-input'; } } else { $attrs['class'] = 'mw-ui-input'; } if ( $wgUseMediaWikiUIEverywhere ) { // Note that size can effect the desired width rendering of mw-ui-input elements // so it is removed. Left intact when mediawiki ui not enabled. unset( $attrs['size'] ); } return $attrs; } /** * Returns an HTML element in a string. The major advantage here over * manually typing out the HTML is that it will escape all attribute * values. If you're hardcoding all the attributes, or there are none, you * should probably just type out the html element yourself. * * This is quite similar to Xml::tags(), but it implements some useful * HTML-specific logic. For instance, there is no $allowShortTag * parameter: the closing tag is magically omitted if $element has an empty * content model. If $wgWellFormedXml is false, then a few bytes will be * shaved off the HTML output as well. * * @param string $element The element's name, e.g., 'a' * @param array $attribs Associative array of attributes, e.g., array( * 'href' => 'http://www.mediawiki.org/' ). See expandAttributes() for * further documentation. * @param string $contents The raw HTML contents of the element: *not* * escaped! * @return string Raw HTML */ public static function rawElement( $element, $attribs = array(), $contents = '' ) { global $wgWellFormedXml; $start = self::openElement( $element, $attribs ); if ( in_array( $element, self::$voidElements ) ) { if ( $wgWellFormedXml ) { // Silly XML. return substr( $start, 0, -1 ) . ' />'; } return $start; } else { return "$start$contents" . self::closeElement( $element ); } } /** * Identical to rawElement(), but HTML-escapes $contents (like * Xml::element()). * * @param string $element * @param array $attribs * @param string $contents * * @return string */ public static function element( $element, $attribs = array(), $contents = '' ) { return self::rawElement( $element, $attribs, strtr( $contents, array( // There's no point in escaping quotes, >, etc. in the contents of // elements. '&' => '&', '<' => '<' ) ) ); } /** * Identical to rawElement(), but has no third parameter and omits the end * tag (and the self-closing '/' in XML mode for empty elements). * * @param string $element * @param array $attribs * * @return string */ public static function openElement( $element, $attribs = array() ) { global $wgWellFormedXml; $attribs = (array)$attribs; // This is not required in HTML5, but let's do it anyway, for // consistency and better compression. $element = strtolower( $element ); // In text/html, initial and tags can be omitted under // pretty much any sane circumstances, if they have no attributes. See: // if ( !$wgWellFormedXml && !$attribs && in_array( $element, array( 'html', 'head' ) ) ) { return ''; } // Remove invalid input types if ( $element == 'input' ) { $validTypes = array( 'hidden', 'text', 'password', 'checkbox', 'radio', 'file', 'submit', 'image', 'reset', 'button', // HTML input types 'datetime', 'datetime-local', 'date', 'month', 'time', 'week', 'number', 'range', 'email', 'url', 'search', 'tel', 'color', ); if ( isset( $attribs['type'] ) && !in_array( $attribs['type'], $validTypes ) ) { unset( $attribs['type'] ); } } // According to standard the default type for elements is "submit". // Depending on compatibility mode IE might use "button", instead. // We enforce the standard "submit". if ( $element == 'button' && !isset( $attribs['type'] ) ) { $attribs['type'] = 'submit'; } return "<$element" . self::expandAttributes( self::dropDefaults( $element, $attribs ) ) . '>'; } /** * Returns "" * * @since 1.17 * @param string $element Name of the element, e.g., 'a' * @return string A closing tag */ public static function closeElement( $element ) { $element = strtolower( $element ); return ""; } /** * Given an element name and an associative array of element attributes, * return an array that is functionally identical to the input array, but * possibly smaller. In particular, attributes might be stripped if they * are given their default values. * * This method is not guaranteed to remove all redundant attributes, only * some common ones and some others selected arbitrarily at random. It * only guarantees that the output array should be functionally identical * to the input array (currently per the HTML 5 draft as of 2009-09-06). * * @param string $element Name of the element, e.g., 'a' * @param array $attribs Associative array of attributes, e.g., array( * 'href' => 'http://www.mediawiki.org/' ). See expandAttributes() for * further documentation. * @return array An array of attributes functionally identical to $attribs */ private static function dropDefaults( $element, $attribs ) { // Whenever altering this array, please provide a covering test case // in HtmlTest::provideElementsWithAttributesHavingDefaultValues static $attribDefaults = array( 'area' => array( 'shape' => 'rect' ), 'button' => array( 'formaction' => 'GET', 'formenctype' => 'application/x-www-form-urlencoded', ), 'canvas' => array( 'height' => '150', 'width' => '300', ), 'command' => array( 'type' => 'command' ), 'form' => array( 'action' => 'GET', 'autocomplete' => 'on', 'enctype' => 'application/x-www-form-urlencoded', ), 'input' => array( 'formaction' => 'GET', 'type' => 'text', ), 'keygen' => array( 'keytype' => 'rsa' ), 'link' => array( 'media' => 'all' ), 'menu' => array( 'type' => 'list' ), // Note: the use of text/javascript here instead of other JavaScript // MIME types follows the HTML5 spec. 'script' => array( 'type' => 'text/javascript' ), 'style' => array( 'media' => 'all', 'type' => 'text/css', ), 'textarea' => array( 'wrap' => 'soft' ), ); $element = strtolower( $element ); foreach ( $attribs as $attrib => $value ) { $lcattrib = strtolower( $attrib ); if ( is_array( $value ) ) { $value = implode( ' ', $value ); } else { $value = strval( $value ); } // Simple checks using $attribDefaults if ( isset( $attribDefaults[$element][$lcattrib] ) && $attribDefaults[$element][$lcattrib] == $value ) { unset( $attribs[$attrib] ); } if ( $lcattrib == 'class' && $value == '' ) { unset( $attribs[$attrib] ); } } // More subtle checks if ( $element === 'link' && isset( $attribs['type'] ) && strval( $attribs['type'] ) == 'text/css' ) { unset( $attribs['type'] ); } if ( $element === 'input' ) { $type = isset( $attribs['type'] ) ? $attribs['type'] : null; $value = isset( $attribs['value'] ) ? $attribs['value'] : null; if ( $type === 'checkbox' || $type === 'radio' ) { // The default value for checkboxes and radio buttons is 'on' // not ''. By stripping value="" we break radio boxes that // actually wants empty values. if ( $value === 'on' ) { unset( $attribs['value'] ); } } elseif ( $type === 'submit' ) { // The default value for submit appears to be "Submit" but // let's not bother stripping out localized text that matches // that. } else { // The default value for nearly every other field type is '' // The 'range' and 'color' types use different defaults but // stripping a value="" does not hurt them. if ( $value === '' ) { unset( $attribs['value'] ); } } } if ( $element === 'select' && isset( $attribs['size'] ) ) { if ( in_array( 'multiple', $attribs ) || ( isset( $attribs['multiple'] ) && $attribs['multiple'] !== false ) ) { // A multi-select if ( strval( $attribs['size'] ) == '4' ) { unset( $attribs['size'] ); } } else { // Single select if ( strval( $attribs['size'] ) == '1' ) { unset( $attribs['size'] ); } } } return $attribs; } /** * Given an associative array of element attributes, generate a string * to stick after the element name in HTML output. Like array( 'href' => * 'http://www.mediawiki.org/' ) becomes something like * ' href="http://www.mediawiki.org"'. Again, this is like * Xml::expandAttributes(), but it implements some HTML-specific logic. * For instance, it will omit quotation marks if $wgWellFormedXml is false, * and will treat boolean attributes specially. * * Attributes that can contain space-separated lists ('class', 'accesskey' and 'rel') array * values are allowed as well, which will automagically be normalized * and converted to a space-separated string. In addition to a numerical * array, the attribute value may also be an associative array. See the * example below for how that works. * * @par Numerical array * @code * Html::element( 'em', array( * 'class' => array( 'foo', 'bar' ) * ) ); * // gives '' * @endcode * * @par Associative array * @code * Html::element( 'em', array( * 'class' => array( 'foo', 'bar', 'foo' => false, 'quux' => true ) * ) ); * // gives '' * @endcode * * @param array $attribs Associative array of attributes, e.g., array( * 'href' => 'http://www.mediawiki.org/' ). Values will be HTML-escaped. * A value of false means to omit the attribute. For boolean attributes, * you can omit the key, e.g., array( 'checked' ) instead of * array( 'checked' => 'checked' ) or such. * * @throws MWException If an attribute that doesn't allow lists is set to an array * @return string HTML fragment that goes between element name and '>' * (starting with a space if at least one attribute is output) */ public static function expandAttributes( $attribs ) { global $wgWellFormedXml; $ret = ''; $attribs = (array)$attribs; foreach ( $attribs as $key => $value ) { // Support intuitive array( 'checked' => true/false ) form if ( $value === false || is_null( $value ) ) { continue; } // For boolean attributes, support array( 'foo' ) instead of // requiring array( 'foo' => 'meaningless' ). if ( is_int( $key ) && in_array( strtolower( $value ), self::$boolAttribs ) ) { $key = $value; } // Not technically required in HTML5 but we'd like consistency // and better compression anyway. $key = strtolower( $key ); // Bug 23769: Blacklist all form validation attributes for now. Current // (June 2010) WebKit has no UI, so the form just refuses to submit // without telling the user why, which is much worse than failing // server-side validation. Opera is the only other implementation at // this time, and has ugly UI, so just kill the feature entirely until // we have at least one good implementation. // As the default value of "1" for "step" rejects decimal // numbers to be entered in 'type="number"' fields, allow // the special case 'step="any"'. if ( in_array( $key, array( 'max', 'min', 'pattern', 'required' ) ) || $key === 'step' && $value !== 'any' ) { continue; } // http://www.w3.org/TR/html401/index/attributes.html ("space-separated") // http://www.w3.org/TR/html5/index.html#attributes-1 ("space-separated") $spaceSeparatedListAttributes = array( 'class', // html4, html5 'accesskey', // as of html5, multiple space-separated values allowed // html4-spec doesn't document rel= as space-separated // but has been used like that and is now documented as such // in the html5-spec. 'rel', ); // Specific features for attributes that allow a list of space-separated values if ( in_array( $key, $spaceSeparatedListAttributes ) ) { // Apply some normalization and remove duplicates // Convert into correct array. Array can contain space-separated // values. Implode/explode to get those into the main array as well. if ( is_array( $value ) ) { // If input wasn't an array, we can skip this step $newValue = array(); foreach ( $value as $k => $v ) { if ( is_string( $v ) ) { // String values should be normal `array( 'foo' )` // Just append them if ( !isset( $value[$v] ) ) { // As a special case don't set 'foo' if a // separate 'foo' => true/false exists in the array // keys should be authoritative $newValue[] = $v; } } elseif ( $v ) { // If the value is truthy but not a string this is likely // an array( 'foo' => true ), falsy values don't add strings $newValue[] = $k; } } $value = implode( ' ', $newValue ); } $value = explode( ' ', $value ); // Normalize spacing by fixing up cases where people used // more than 1 space and/or a trailing/leading space $value = array_diff( $value, array( '', ' ' ) ); // Remove duplicates and create the string $value = implode( ' ', array_unique( $value ) ); } elseif ( is_array( $value ) ) { throw new MWException( "HTML attribute $key can not contain a list of values" ); } // See the "Attributes" section in the HTML syntax part of HTML5, // 9.1.2.3 as of 2009-08-10. Most attributes can have quotation // marks omitted, but not all. (Although a literal " is not // permitted, we don't check for that, since it will be escaped // anyway.) # // See also research done on further characters that need to be // escaped: http://code.google.com/p/html5lib/issues/detail?id=93 $badChars = "\\x00- '=<>`/\x{00a0}\x{1680}\x{180e}\x{180F}\x{2000}\x{2001}" . "\x{2002}\x{2003}\x{2004}\x{2005}\x{2006}\x{2007}\x{2008}\x{2009}" . "\x{200A}\x{2028}\x{2029}\x{202F}\x{205F}\x{3000}"; if ( $wgWellFormedXml || $value === '' || preg_match( "![$badChars]!u", $value ) ) { $quote = '"'; } else { $quote = ''; } if ( in_array( $key, self::$boolAttribs ) ) { // In HTML5, we can leave the value empty. If we don't need // well-formed XML, we can omit the = entirely. if ( !$wgWellFormedXml ) { $ret .= " $key"; } else { $ret .= " $key=\"\""; } } else { // Apparently we need to entity-encode \n, \r, \t, although the // spec doesn't mention that. Since we're doing strtr() anyway, // and we don't need <> escaped here, we may as well not call // htmlspecialchars(). // @todo FIXME: Verify that we actually need to // escape \n\r\t here, and explain why, exactly. # // We could call Sanitizer::encodeAttribute() for this, but we // don't because we're stubborn and like our marginal savings on // byte size from not having to encode unnecessary quotes. $map = array( '&' => '&', '"' => '"', "\n" => ' ', "\r" => ' ', "\t" => ' ' ); if ( $wgWellFormedXml ) { // This is allowed per spec: // But reportedly it breaks some XML tools? // @todo FIXME: Is this really true? $map['<'] = '<'; } $ret .= " $key=$quote" . strtr( $value, $map ) . $quote; } } return $ret; } /** * Output a "" or (for XML) literal "]]>". * * @param string $contents JavaScript * @return string Raw HTML */ public static function inlineScript( $contents ) { global $wgWellFormedXml; $attrs = array(); if ( $wgWellFormedXml && preg_match( '/[<&]/', $contents ) ) { $contents = "/**/"; } return self::rawElement( 'script', $attrs, $contents ); } /** * Output a "". * * @param string $url * @return string Raw HTML */ public static function linkedScript( $url ) { $attrs = array( 'src' => $url ); return self::element( 'script', $attrs ); } /** * Output a "" (admittedly unlikely). * * @param string $contents CSS * @param string $media A media type string, like 'screen' * @return string Raw HTML */ public static function inlineStyle( $contents, $media = 'all' ) { global $wgWellFormedXml; if ( $wgWellFormedXml && preg_match( '/[<&]/', $contents ) ) { $contents = "/**/"; } return self::rawElement( 'style', array( 'type' => 'text/css', 'media' => $media, ), $contents ); } /** * Output a "" linking to the given URL for the given * media type (if any). * * @param string $url * @param string $media A media type string, like 'screen' * @return string Raw HTML */ public static function linkedStyle( $url, $media = 'all' ) { return self::element( 'link', array( 'rel' => 'stylesheet', 'href' => $url, 'type' => 'text/css', 'media' => $media, ) ); } /** * Convenience function to produce an "" element. This supports the * new HTML5 input types and attributes. * * @param string $name Name attribute * @param array $value Value attribute * @param string $type Type attribute * @param array $attribs Associative array of miscellaneous extra * attributes, passed to Html::element() * @return string Raw HTML */ public static function input( $name, $value = '', $type = 'text', $attribs = array() ) { $attribs['type'] = $type; $attribs['value'] = $value; $attribs['name'] = $name; if ( in_array( $type, array( 'text', 'search', 'email', 'password', 'number' ) ) ) { $attribs = Html::getTextInputAttributes( $attribs ); } return self::element( 'input', $attribs ); } /** * Convenience function to produce a checkbox (input element with type=checkbox) * * @param string $name Name attribute * @param bool $checked Whether the checkbox is checked or not * @param array $attribs Array of additional attributes * @return string */ public static function check( $name, $checked = false, array $attribs = array() ) { if ( isset( $attribs['value'] ) ) { $value = $attribs['value']; unset( $attribs['value'] ); } else { $value = 1; } if ( $checked ) { $attribs[] = 'checked'; } return self::input( $name, $value, 'checkbox', $attribs ); } /** * Convenience function to produce a checkbox (input element with type=checkbox) * * @param string $name Name attribute * @param bool $checked Whether the checkbox is checked or not * @param array $attribs Array of additional attributes * @return string */ public static function radio( $name, $checked = false, array $attribs = array() ) { if ( isset( $attribs['value'] ) ) { $value = $attribs['value']; unset( $attribs['value'] ); } else { $value = 1; } if ( $checked ) { $attribs[] = 'checked'; } return self::input( $name, $value, 'radio', $attribs ); } /** * Convenience function for generating a label for inputs. * * @param string $label Contents of the label * @param string $id ID of the element being labeled * @param array $attribs Additional attributes * @return string */ public static function label( $label, $id, array $attribs = array() ) { $attribs += array( 'for' => $id ); return self::element( 'label', $attribs, $label ); } /** * Convenience function to produce an input element with type=hidden * * @param string $name Name attribute * @param string $value Value attribute * @param array $attribs Associative array of miscellaneous extra * attributes, passed to Html::element() * @return string Raw HTML */ public static function hidden( $name, $value, $attribs = array() ) { return self::input( $name, $value, 'hidden', $attribs ); } /** * Convenience function to produce a element. * * This supports leaving out the cols= and rows= which Xml requires and are * required by HTML4/XHTML but not required by HTML5. * * @param string $name Name attribute * @param string $value Value attribute * @param array $attribs Associative array of miscellaneous extra * attributes, passed to Html::element() * @return string Raw HTML */ public static function textarea( $name, $value = '', $attribs = array() ) { $attribs['name'] = $name; if ( substr( $value, 0, 1 ) == "\n" ) { // Workaround for bug 12130: browsers eat the initial newline // assuming that it's just for show, but they do keep the later // newlines, which we may want to preserve during editing. // Prepending a single newline $spacedValue = "\n" . $value; } else { $spacedValue = $value; } return self::element( 'textarea', Html::getTextInputAttributes( $attribs ), $spacedValue ); } /** * Build a drop-down box for selecting a namespace * * @param array $params Params to set. * - selected: [optional] Id of namespace which should be pre-selected * - all: [optional] Value of item for "all namespaces". If null or unset, * no "<option>" is generated to select all namespaces. * - label: text for label to add before the field. * - exclude: [optional] Array of namespace ids to exclude. * - disable: [optional] Array of namespace ids for which the option should * be disabled in the selector. * @param array $selectAttribs HTML attributes for the generated select element. * - id: [optional], default: 'namespace'. * - name: [optional], default: 'namespace'. * @return string HTML code to select a namespace. */ public static function namespaceSelector( array $params = array(), array $selectAttribs = array() ) { global $wgContLang; ksort( $selectAttribs ); // Is a namespace selected? if ( isset( $params['selected'] ) ) { // If string only contains digits, convert to clean int. Selected could also // be "all" or "" etc. which needs to be left untouched. // PHP is_numeric() has issues with large strings, PHP ctype_digit has other issues // and returns false for already clean ints. Use regex instead.. if ( preg_match( '/^\d+$/', $params['selected'] ) ) { $params['selected'] = intval( $params['selected'] ); } // else: leaves it untouched for later processing } else { $params['selected'] = ''; } if ( !isset( $params['exclude'] ) || !is_array( $params['exclude'] ) ) { $params['exclude'] = array(); } if ( !isset( $params['disable'] ) || !is_array( $params['disable'] ) ) { $params['disable'] = array(); } // Associative array between option-values and option-labels $options = array(); if ( isset( $params['all'] ) ) { // add an option that would let the user select all namespaces. // Value is provided by user, the name shown is localized for the user. $options[$params['all']] = wfMessage( 'namespacesall' )->text(); } // Add all namespaces as options (in the content language) $options += $wgContLang->getFormattedNamespaces(); // Convert $options to HTML and filter out namespaces below 0 $optionsHtml = array(); foreach ( $options as $nsId => $nsName ) { if ( $nsId < NS_MAIN || in_array( $nsId, $params['exclude'] ) ) { continue; } if ( $nsId === NS_MAIN ) { // For other namespaces use use the namespace prefix as label, but for // main we don't use "" but the user message describing it (e.g. "(Main)" or "(Article)") $nsName = wfMessage( 'blanknamespace' )->text(); } elseif ( is_int( $nsId ) ) { $nsName = $wgContLang->convertNamespace( $nsId ); } $optionsHtml[] = Html::element( 'option', array( 'disabled' => in_array( $nsId, $params['disable'] ), 'value' => $nsId, 'selected' => $nsId === $params['selected'], ), $nsName ); } if ( !array_key_exists( 'id', $selectAttribs ) ) { $selectAttribs['id'] = 'namespace'; } if ( !array_key_exists( 'name', $selectAttribs ) ) { $selectAttribs['name'] = 'namespace'; } $ret = ''; if ( isset( $params['label'] ) ) { $ret .= Html::element( 'label', array( 'for' => isset( $selectAttribs['id'] ) ? $selectAttribs['id'] : null, ), $params['label'] ) . ' '; } // Wrap options in a <select> $ret .= Html::openElement( 'select', $selectAttribs ) . "\n" . implode( "\n", $optionsHtml ) . "\n" . Html::closeElement( 'select' ); return $ret; } /** * Constructs the opening html-tag with necessary doctypes depending on * global variables. * * @param array $attribs Associative array of miscellaneous extra * attributes, passed to Html::element() of html tag. * @return string Raw HTML */ public static function htmlHeader( $attribs = array() ) { $ret = ''; global $wgHtml5Version, $wgMimeType, $wgXhtmlNamespaces; $isXHTML = self::isXmlMimeType( $wgMimeType ); if ( $isXHTML ) { // XHTML5 // XML MIME-typed markup should have an xml header. // However a DOCTYPE is not needed. $ret .= "<?xml version=\"1.0\" encoding=\"UTF-8\" ?" . ">\n"; // Add the standard xmlns $attribs['xmlns'] = 'http://www.w3.org/1999/xhtml'; // And support custom namespaces foreach ( $wgXhtmlNamespaces as $tag => $ns ) { $attribs["xmlns:$tag"] = $ns; } } else { // HTML5 // DOCTYPE $ret .= "<!DOCTYPE html>\n"; } if ( $wgHtml5Version ) { $attribs['version'] = $wgHtml5Version; } $html = Html::openElement( 'html', $attribs ); if ( $html ) { $html .= "\n"; } $ret .= $html; return $ret; } /** * Determines if the given MIME type is xml. * * @param string $mimetype MIME type * @return bool */ public static function isXmlMimeType( $mimetype ) { # http://www.whatwg.org/html/infrastructure.html#xml-mime-type # * text/xml # * application/xml # * Any MIME type with a subtype ending in +xml (this implicitly includes application/xhtml+xml) return (bool)preg_match( '!^(text|application)/xml$|^.+/.+\+xml$!', $mimetype ); } /** * Get HTML for an info box with an icon. * * @param string $text Wikitext, get this with wfMessage()->plain() * @param string $icon Path to icon file (used as 'src' attribute) * @param string $alt Alternate text for the icon * @param string $class Additional class name to add to the wrapper div * * @return string */ static function infoBox( $text, $icon, $alt, $class = false ) { $s = Html::openElement( 'div', array( 'class' => "mw-infobox $class" ) ); $s .= Html::openElement( 'div', array( 'class' => 'mw-infobox-left' ) ) . Html::element( 'img', array( 'src' => $icon, 'alt' => $alt, ) ) . Html::closeElement( 'div' ); $s .= Html::openElement( 'div', array( 'class' => 'mw-infobox-right' ) ) . $text . Html::closeElement( 'div' ); $s .= Html::element( 'div', array( 'style' => 'clear: left;' ), ' ' ); $s .= Html::closeElement( 'div' ); $s .= Html::element( 'div', array( 'style' => 'clear: left;' ), ' ' ); return $s; } /** * Generate a srcset attribute value from an array mapping pixel densities * to URLs. Note that srcset supports width and height values as well, which * are not used here. * * @param array $urls * @return string */ static function srcSet( $urls ) { $candidates = array(); foreach ( $urls as $density => $url ) { // Image candidate syntax per current whatwg live spec, 2012-09-23: // http://www.whatwg.org/html/embedded-content-1.html#attr-img-srcset $candidates[] = "{$url} {$density}x"; } return implode( ", ", $candidates ); } }