Merge "Refactor Watchlist code so mobile can be more consistent"

[mediawiki.git] / includes / Html.php

<?php
/**
 * Collection of methods to generate HTML content
 *
 * Copyright © 2009 Aryeh Gregor
 * http://www.mediawiki.org/
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License along
 * with this program; if not, write to the Free Software Foundation, Inc.,
 * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
 * http://www.gnu.org/copyleft/gpl.html
 *
 * @file
 */

/**
 * This class is a collection of static functions that serve two purposes:
 *
 * 1) Implement any algorithms specified by HTML5, or other HTML
 * specifications, in a convenient and self-contained way.
 *
 * 2) Allow HTML elements to be conveniently and safely generated, like the
 * current Xml class but a) less confused (Xml supports HTML-specific things,
 * but only sometimes!) and b) not necessarily confined to XML-compatible
 * output.
 *
 * There are two important configuration options this class uses:
 *
 * $wgMimeType: If this is set to an xml mimetype then output should be
 *     valid XHTML5.
 * $wgWellFormedXml: If this is set to true, then all output should be
 *     well-formed XML (quotes on attributes, self-closing tags, etc.).
 *
 * This class is meant to be confined to utility functions that are called from
 * trusted code paths.  It does not do enforcement of policy like not allowing
 * <a> 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',
        );

        /**
         * 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.
                        '&' => '&amp;',
                        '<' => '&lt;'
                ) ) );
        }

        /**
         * 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 <html> and <head> tags can be omitted under
                // pretty much any sane circumstances, if they have no attributes.  See:
                // <http://www.whatwg.org/html/syntax.html#optional-tags>
                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 <button> 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 "</$element>", except if $wgWellFormedXml is off, in which case
         * it returns the empty string when that's guaranteed to be safe.
         *
         * @since 1.17
         * @param string $element Name of the element, e.g., 'a'
         * @return string A closing tag, if required
         */
        public static function closeElement( $element ) {
                global $wgWellFormedXml;

                $element = strtolower( $element );

                // Reference:
                // http://www.whatwg.org/html/syntax.html#optional-tags
                if ( !$wgWellFormedXml && in_array( $element, array(
                        'html',
                        'head',
                        'body',
                        'li',
                        'dt',
                        'dd',
                        'tr',
                        'td',
                        'th',
                ) ) ) {
                        return '';
                }
                return "</$element>";
        }

        /**
         * 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 '<em class="foo bar"></em>'
         * @endcode
         *
         * @par Associative array
         * @code
         *     Html::element( 'em', array(
         *         'class' => array( 'foo', 'bar', 'foo' => false, 'quux' => true )
         *     ) );
         *     // gives '<em class="bar quux"></em>'
         * @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(
                                        '&' => '&amp;',
                                        '"' => '&quot;',
                                        "\n" => '&#10;',
                                        "\r" => '&#13;',
                                        "\t" => '&#9;'
                                );
                                if ( $wgWellFormedXml ) {
                                        // This is allowed per spec: <http://www.w3.org/TR/xml/#NT-AttValue>
                                        // But reportedly it breaks some XML tools?
                                        // @todo FIXME: Is this really true?
                                        $map['<'] = '&lt;';
                                }
                                $ret .= " $key=$quote" . strtr( $value, $map ) . $quote;
                        }
                }
                return $ret;
        }

        /**
         * Output a "<script>" tag with the given contents.
         *
         * @todo do some useful escaping as well, like if $contents contains
         * literal "</script>" 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 ) ) {
                        $contents = "/*<![CDATA[*/$contents/*]]>*/";
                }

                return self::rawElement( 'script', $attrs, $contents );
        }

        /**
         * Output a "<script>" tag linking to the given URL, e.g.,
         * "<script src=foo.js></script>".
         *
         * @param string $url
         * @return string Raw HTML
         */
        public static function linkedScript( $url ) {
                $attrs = array( 'src' => $url );

                return self::element( 'script', $attrs );
        }

        /**
         * Output a "<style>" tag with the given contents for the given media type
         * (if any).  TODO: do some useful escaping as well, like if $contents
         * contains literal "</style>" (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 ) ) {
                        $contents = "/*<![CDATA[*/$contents/*]]>*/";
                }

                return self::rawElement( 'style', array(
                        'type' => 'text/css',
                        'media' => $media,
                ), $contents );
        }

        /**
         * Output a "<link rel=stylesheet>" 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 "<input>" 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;

                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
         */
        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
         */
        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
         */
        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 <textarea> 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', $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']
                        ) . '&#160;';
                }

                // 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 mimetyped 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 MimeType
         * @return bool
         */
        public static function isXmlMimeType( $mimetype ) {
                # http://www.whatwg.org/html/infrastructure.html#xml-mime-type
                # * text/xml
                # * application/xml
                # * Any mimetype with a subtype ending in +xml (this implicitly includes application/xhtml+xml)
                return (bool)preg_match( '!^(text|application)/xml$|^.+/.+\+xml$!', $mimetype );
        }

        /**
         * Get HTML for an info box with an icon.
         *
         * @param string $text Wikitext, get this with wfMessage()->plain()
         * @param string $icon Icon name, file in skins/common/images
         * @param string $alt Alternate text for the icon
         * @param string $class Additional class name to add to the wrapper div
         * @param bool $useStylePath
         *
         * @return string
         */
        static function infoBox( $text, $icon, $alt, $class = false, $useStylePath = true ) {
                global $wgStylePath;

                if ( $useStylePath ) {
                        $icon = $wgStylePath . '/common/images/' . $icon;
                }

                $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 );
        }
}