htmlpurifier/library/HTMLPurifier/AttrDef/HTML/ID.php

<?php

/**
 * Validates the HTML attribute ID.
 * @warning Even though this is the id processor, it
 *          will ignore the directive Attr:IDBlacklist, since it will only
 *          go according to the ID accumulator. Since the accumulator is
 *          automatically generated, it will have already absorbed the
 *          blacklist. If you're hacking around, make sure you use load()!
 */

class HTMLPurifier_AttrDef_HTML_ID extends HTMLPurifier_AttrDef
{

    // ref functionality disabled, since we also have to verify
    // whether or not the ID it refers to exists

    public function validate($id, $config, $context) {

        if (!$config->get('Attr', 'EnableID')) return false;

        $id = trim($id); // trim it first

        if ($id === '') return false;

        $prefix = $config->get('Attr', 'IDPrefix');
        if ($prefix !== '') {
            $prefix .= $config->get('Attr', 'IDPrefixLocal');
            // prevent re-appending the prefix
            if (strpos($id, $prefix) !== 0) $id = $prefix . $id;
        } elseif ($config->get('Attr', 'IDPrefixLocal') !== '') {
            trigger_error('%Attr.IDPrefixLocal cannot be used unless '.
                '%Attr.IDPrefix is set', E_USER_WARNING);
        }

        //if (!$this->ref) {
            $id_accumulator =& $context->get('IDAccumulator');
            if (isset($id_accumulator->ids[$id])) return false;
        //}

        // we purposely avoid using regex, hopefully this is faster

        if (ctype_alpha($id)) {
            $result = true;
        } else {
            if (!ctype_alpha(@$id[0])) return false;
            $trim = trim( // primitive style of regexps, I suppose
                $id,
                'A..Za..z0..9:-._'
              );
            $result = ($trim === '');
        }

        $regexp = $config->get('Attr', 'IDBlacklistRegexp');
        if ($regexp && preg_match($regexp, $id)) {
            return false;
        }

        if (/*!$this->ref && */$result) $id_accumulator->add($id);

        // if no change was made to the ID, return the result
        // else, return the new id if stripping whitespace made it
        //     valid, or return false.
        return $result ? $id : false;

    }

}