excel/vendor/ezyang/htmlpurifier/library/HTMLPurifier/Config.php

<?php

/**
 * Configuration object that triggers customizable behavior.
 *
 * @warning This class is strongly defined: that means that the class
 *          will fail if an undefined directive is retrieved or set.
 *
 * @note Many classes that could (although many times don't) use the
 *       configuration object make it a mandatory parameter.  This is
 *       because a configuration object should always be forwarded,
 *       otherwise, you run the risk of missing a parameter and then
 *       being stumped when a configuration directive doesn't work.
 *
 * @todo Reconsider some of the public member variables
 */
class HTMLPurifier_Config
{

    /**
     * HTML Purifier's version
     * @type string
     */
    public $version = '4.15.0';

    /**
     * Whether or not to automatically finalize
     * the object if a read operation is done.
     * @type bool
     */
    public $autoFinalize = true;

    // protected member variables

    /**
     * Namespace indexed array of serials for specific namespaces.
     * @see getSerial() for more info.
     * @type string[]
     */
    protected $serials = array();

    /**
     * Serial for entire configuration object.
     * @type string
     */
    protected $serial;

    /**
     * Parser for variables.
     * @type HTMLPurifier_VarParser_Flexible
     */
    protected $parser = null;

    /**
     * Reference HTMLPurifier_ConfigSchema for value checking.
     * @type HTMLPurifier_ConfigSchema
     * @note This is public for introspective purposes. Please don't
     *       abuse!
     */
    public $def;

    /**
     * Indexed array of definitions.
     * @type HTMLPurifier_Definition[]
     */
    protected $definitions;

    /**
     * Whether or not config is finalized.
     * @type bool
     */
    protected $finalized = false;

    /**
     * Property list containing configuration directives.
     * @type array
     */
    protected $plist;

    /**
     * Whether or not a set is taking place due to an alias lookup.
     * @type bool
     */
    private $aliasMode;

    /**
     * Set to false if you do not want line and file numbers in errors.
     * (useful when unit testing).  This will also compress some errors
     * and exceptions.
     * @type bool
     */
    public $chatty = true;

    /**
     * Current lock; only gets to this namespace are allowed.
     * @type string
     */
    private $lock;

    /**
     * Constructor
     * @param HTMLPurifier_ConfigSchema $definition ConfigSchema that defines
     * what directives are allowed.
     * @param HTMLPurifier_PropertyList $parent
     */
    public function __construct($definition, $parent = null)
    {
        $parent = $parent ? $parent : $definition->defaultPlist;
        $this->plist = new HTMLPurifier_PropertyList($parent);
        $this->def = $definition; // keep a copy around for checking
        $this->parser = new HTMLPurifier_VarParser_Flexible();
    }

    /**
     * Convenience constructor that creates a config object based on a mixed var
     * @param mixed $config Variable that defines the state of the config
     *                      object. Can be: a HTMLPurifier_Config() object,
     *                      an array of directives based on loadArray(),
     *                      or a string filename of an ini file.
     * @param HTMLPurifier_ConfigSchema $schema Schema object
     * @return HTMLPurifier_Config Configured object
     */
    public static function create($config, $schema = null)
    {
        if ($config instanceof HTMLPurifier_Config) {
            // pass-through
            return $config;
        }
        if (!$schema) {
            $ret = HTMLPurifier_Config::createDefault();
        } else {
            $ret = new HTMLPurifier_Config($schema);
        }
        if (is_string($config)) {
            $ret->loadIni($config);
        } elseif (is_array($config)) $ret->loadArray($config);
        return $ret;
    }

    /**
     * Creates a new config object that inherits from a previous one.
     * @param HTMLPurifier_Config $config Configuration object to inherit from.
     * @return HTMLPurifier_Config object with $config as its parent.
     */
    public static function inherit(HTMLPurifier_Config $config)
    {
        return new HTMLPurifier_Config($config->def, $config->plist);
    }

    /**
     * Convenience constructor that creates a default configuration object.
     * @return HTMLPurifier_Config default object.
     */
    public static function createDefault()
    {
        $definition = HTMLPurifier_ConfigSchema::instance();
        $config = new HTMLPurifier_Config($definition);
        return $config;
    }

    /**
     * Retrieves a value from the configuration.
     *
     * @param string $key String key
     * @param mixed $a
     *
     * @return mixed
     */
    public function get($key, $a = null)
    {
        if ($a !== null) {
            $this->triggerError(
                "Using deprecated API: use \$config->get('$key.$a') instead",
                E_USER_WARNING
            );
            $key = "$key.$a";
        }
        if (!$this->finalized) {
            $this->autoFinalize();
        }
        if (!isset($this->def->info[$key])) {
            // can't add % due to SimpleTest bug
            $this->triggerError(
                'Cannot retrieve value of undefined directive ' . htmlspecialchars($key),
                E_USER_WARNING
            );
            return;
        }
        if (isset($this->def->info[$key]->isAlias)) {
            $d = $this->def->info[$key];
            $this->triggerError(
                'Cannot get value from aliased directive, use real name ' . $d->key,
                E_USER_ERROR
            );
            return;
        }
        if ($this->lock) {
            list($ns) = explode('.', $key);
            if ($ns !== $this->lock) {
                $this->triggerError(
                    'Cannot get value of namespace ' . $ns . ' when lock for ' .
                    $this->lock .
                    ' is active, this probably indicates a Definition setup method ' .
                    'is accessing directives that are not within its namespace',
                    E_USER_ERROR
                );
                return;
            }
        }
        return $this->plist->get($key);
    }

    /**
     * Retrieves an array of directives to values from a given namespace
     *
     * @param string $namespace String namespace
     *
     * @return array
     */
    public function getBatch($namespace)
    {
        if (!$this->finalized) {
            $this->autoFinalize();
        }
        $full = $this->getAll();
        if (!isset($full[$namespace])) {
            $this->triggerError(
                'Cannot retrieve undefined namespace ' .
                htmlspecialchars($namespace),
                E_USER_WARNING
            );
            return;
        }
        return $full[$namespace];
    }

    /**
     * Returns a SHA-1 signature of a segment of the configuration object
     * that uniquely identifies that particular configuration
     *
     * @param string $namespace Namespace to get serial for
     *
     * @return string
     * @note Revision is handled specially and is removed from the batch
     *       before processing!
     */
    public function getBatchSerial($namespace)
    {
        if (empty($this->serials[$namespace])) {
            $batch = $this->getBatch($namespace);
            unset($batch['DefinitionRev']);
            $this->serials[$namespace] = sha1(serialize($batch));
        }
        return $this->serials[$namespace];
    }

    /**
     * Returns a SHA-1 signature for the entire configuration object
     * that uniquely identifies that particular configuration
     *
     * @return string
     */
    public function getSerial()
    {
        if (empty($this->serial)) {
            $this->serial = sha1(serialize($this->getAll()));
        }
        return $this->serial;
    }

    /**
     * Retrieves all directives, organized by namespace
     *
     * @warning This is a pretty inefficient function, avoid if you can
     */
    public function getAll()
    {
        if (!$this->finalized) {
            $this->autoFinalize();
        }
        $ret = array();
        foreach ($this->plist->squash() as $name => $value) {
            list($ns, $key) = explode('.', $name, 2);
            $ret[$ns][$key] = $value;
        }
        return $ret;
    }

    /**
     * Sets a value to configuration.
     *
     * @param string $key key
     * @param mixed $value value
     * @param mixed $a
     */
    public function set($key, $value, $a = null)
    {
        if (strpos($key, '.') === false) {
            $namespace = $key;
            $directive = $value;
            $value = $a;
            $key = "$key.$directive";
            $this->triggerError("Using deprecated API: use \$config->set('$key', ...) instead", E_USER_NOTICE);
        } else {
            list($namespace) = explode('.', $key);
        }
        if ($this->isFinalized('Cannot set directive after finalization')) {
            return;
        }
        if (!isset($this->def->info[$key])) {
            $this->triggerError(
                'Cannot set undefined directive ' . htmlspecialchars($key) . ' to value',
                E_USER_WARNING
            );
            return;
        }
        $def = $this->def->info[$key];

        if (isset($def->isAlias)) {
            if ($this->aliasMode) {
                $this->triggerError(
                    'Double-aliases not allowed, please fix '.
                    'ConfigSchema bug with' . $key,
                    E_USER_ERROR
                );
                return;
            }
            $this->aliasMode = true;
            $this->set($def->key, $value);
            $this->aliasMode = false;
            $this->triggerError("$key is an alias, preferred directive name is {$def->key}", E_USER_NOTICE);
            return;
        }

        // Raw type might be negative when using the fully optimized form
        // of stdClass, which indicates allow_null == true
        $rtype = is_int($def) ? $def : $def->type;
        if ($rtype < 0) {
            $type = -$rtype;
            $allow_null = true;
        } else {
            $type = $rtype;
            $allow_null = isset($def->allow_null);
        }

        try {
            $value = $this->parser->parse($value, $type, $allow_null);
        } catch (HTMLPurifier_VarParserException $e) {
            $this->triggerError(
                'Value for ' . $key . ' is of invalid type, should be ' .
                HTMLPurifier_VarParser::getTypeName($type),
                E_USER_WARNING
            );
            return;
        }
        if (is_string($value) && is_object($def)) {
            // resolve value alias if defined
            if (isset($def->aliases[$value])) {
                $value = $def->aliases[$value];
            }
            // check to see if the value is allowed
            if (isset($def->allowed) && !isset($def->allowed[$value])) {
                $this->triggerError(
                    'Value not supported, valid values are: ' .
                    $this->_listify($def->allowed),
                    E_USER_WARNING
                );
                return;
            }
        }
        $this->plist->set($key, $value);

        // reset definitions if the directives they depend on changed
        // this is a very costly process, so it's discouraged
        // with finalization
        if ($namespace == 'HTML' || $namespace == 'CSS' || $namespace == 'URI') {
            $this->definitions[$namespace] = null;
        }

        $this->serials[$namespace] = false;
    }

    /**
     * Convenience function for error reporting
     *
     * @param array $lookup
     *
     * @return string
     */
    private function _listify($lookup)
    {
        $list = array();
        foreach ($lookup as $name => $b) {
            $list[] = $name;
        }
        return implode(', ', $list);
    }

    /**
     * Retrieves object reference to the HTML definition.
     *
     * @param bool $raw Return a copy that has not been setup yet. Must be
     *             called before it's been setup, otherwise won't work.
     * @param bool $optimized If true, this method may return null, to
     *             indicate that a cached version of the modified
     *             definition object is available and no further edits
     *             are necessary.  Consider using
     *             maybeGetRawHTMLDefinition, which is more explicitly
     *             named, instead.
     *
     * @return HTMLPurifier_HTMLDefinition|null
     */
    public function getHTMLDefinition($raw = false, $optimized = false)
    {
        return $this->getDefinition('HTML', $raw, $optimized);
    }

    /**
     * Retrieves object reference to the CSS definition
     *
     * @param bool $raw Return a copy that has not been setup yet. Must be
     *             called before it's been setup, otherwise won't work.
     * @param bool $optimized If true, this method may return null, to
     *             indicate that a cached version of the modified
     *             definition object is available and no further edits
     *             are necessary.  Consider using
     *             maybeGetRawCSSDefinition, which is more explicitly
     *             named, instead.
     *
     * @return HTMLPurifier_CSSDefinition|null
     */
    public function getCSSDefinition($raw = false, $optimized = false)
    {
        return $this->getDefinition('CSS', $raw, $optimized);
    }

    /**
     * Retrieves object reference to the URI definition
     *
     * @param bool $raw Return a copy that has not been setup yet. Must be
     *             called before it's been setup, otherwise won't work.
     * @param bool $optimized If true, this method may return null, to
     *             indicate that a cached version of the modified
     *             definition object is available and no further edits
     *             are necessary.  Consider using
     *             maybeGetRawURIDefinition, which is more explicitly
     *             named, instead.
     *
     * @return HTMLPurifier_URIDefinition|null
     */
    public function getURIDefinition($raw = false, $optimized = false)
    {
        return $this->getDefinition('URI', $raw, $optimized);
    }

    /**
     * Retrieves a definition
     *
     * @param string $type Type of definition: HTML, CSS, etc
     * @param bool $raw Whether or not definition should be returned raw
     * @param bool $optimized Only has an effect when $raw is true.  Whether
     *        or not to return null if the result is already present in
     *        the cache.  This is off by default for backwards
     *        compatibility reasons, but you need to do things this
     *        way in order to ensure that caching is done properly.
     *        Check out enduser-customize.html for more details.
     *        We probably won't ever change this default, as much as the
     *        maybe semantics is the "right thing to do."
     *
     * @throws HTMLPurifier_Exception
     * @return HTMLPurifier_Definition|null
     */
    public function getDefinition($type, $raw = false, $optimized = false)
    {
        if ($optimized && !$raw) {
            throw new HTMLPurifier_Exception("Cannot set optimized = true when raw = false");
        }
        if (!$this->finalized) {
            $this->autoFinalize();
        }
        // temporarily suspend locks, so we can handle recursive definition calls
        $lock = $this->lock;
        $this->lock = null;
        $factory = HTMLPurifier_DefinitionCacheFactory::instance();
        $cache = $factory->create($type, $this);
        $this->lock = $lock;
        if (!$raw) {
            // full definition
            // ---------------
            // check if definition is in memory
            if (!empty($this->definitions[$type])) {
                $def = $this->definitions[$type];
                // check if the definition is setup
                if ($def->setup) {
                    return $def;
                } else {
                    $def->setup($this);
                    if ($def->optimized) {
                        $cache->add($def, $this);
                    }
                    return $def;
                }
            }
            // check if definition is in cache
            $def = $cache->get($this);
            if ($def) {
                // definition in cache, save to memory and return it
                $this->definitions[$type] = $def;
                return $def;
            }
            // initialize it
            $def = $this->initDefinition($type);
            // set it up
            $this->lock = $type;
            $def->setup($this);
            $this->lock = null;
            // save in cache
            $cache->add($def, $this);
            // return it
            return $def;
        } else {
            // raw definition
            // --------------
            // check preconditions
            $def = null;
            if ($optimized) {
                if (is_null($this->get($type . '.DefinitionID'))) {
                    // fatally error out if definition ID not set
                    throw new HTMLPurifier_Exception(
                        "Cannot retrieve raw version without specifying %$type.DefinitionID"
                    );
                }
            }
            if (!empty($this->definitions[$type])) {
                $def = $this->definitions[$type];
                if ($def->setup && !$optimized) {
                    $extra = $this->chatty ?
                        " (try moving this code block earlier in your initialization)" :
                        "";
                    throw new HTMLPurifier_Exception(
                        "Cannot retrieve raw definition after it has already been setup" .
                        $extra
                    );
                }
                if ($def->optimized === null) {
                    $extra = $this->chatty ? " (try flushing your cache)" : "";
                    throw new HTMLPurifier_Exception(
                        "Optimization status of definition is unknown" . $extra
                    );
                }
                if ($def->optimized !== $optimized) {
                    $msg = $optimized ? "optimized" : "unoptimized";
                    $extra = $this->chatty ?
                        " (this backtrace is for the first inconsistent call, which was for a $msg raw definition)"
                        : "";
                    throw new HTMLPurifier_Exception(
                        "Inconsistent use of optimized and unoptimized raw definition retrievals" . $extra
                    );
                }
            }
            // check if definition was in memory
            if ($def) {
                if ($def->setup) {
                    // invariant: $optimized === true (checked above)
                    return null;
                } else {
                    return $def;
                }
            }
            // if optimized, check if definition was in cache
            // (because we do the memory check first, this formulation
            // is prone to cache slamming, but I think
            // guaranteeing that either /all/ of the raw
            // setup code or /none/ of it is run is more important.)
            if ($optimized) {
                // This code path only gets run once; once we put
                // something in $definitions (which is guaranteed by the
                // trailing code), we always short-circuit above.
                $def = $cache->get($this);
                if ($def) {
                    // save the full definition for later, but don't
                    // return it yet
                    $this->definitions[$type] = $def;
                    return null;
                }
            }
            // check invariants for creation
            if (!$optimized) {
                if (!is_null($this->get($type . '.DefinitionID'))) {
                    if ($this->chatty) {
                        $this->triggerError(
                            'Due to a documentation error in previous version of HTML Purifier, your ' .
                            'definitions are not being cached.  If this is OK, you can remove the ' .
                            '%$type.DefinitionRev and %$type.DefinitionID declaration.  Otherwise, ' .
                            'modify your code to use maybeGetRawDefinition, and test if the returned ' .
                            'value is null before making any edits (if it is null, that means that a ' .
                            'cached version is available, and no raw operations are necessary).  See ' .
                            '<a href="http://htmlpurifier.org/docs/enduser-customize.html#optimized">' .
                            'Customize</a> for more details',
                            E_USER_WARNING
                        );
                    } else {
                        $this->triggerError(
                            "Useless DefinitionID declaration",
                            E_USER_WARNING
                        );
                    }
                }
            }
            // initialize it
            $def = $this->initDefinition($type);
            $def->optimized = $optimized;
            return $def;
        }
        throw new HTMLPurifier_Exception("The impossible happened!");
    }

    /**
     * Initialise definition
     *
     * @param string $type What type of definition to create
     *
     * @return HTMLPurifier_CSSDefinition|HTMLPurifier_HTMLDefinition|HTMLPurifier_URIDefinition
     * @throws HTMLPurifier_Exception
     */
    private function initDefinition($type)
    {
        // quick checks failed, let's create the object
        if ($type == 'HTML') {
            $def = new HTMLPurifier_HTMLDefinition();
        } elseif ($type == 'CSS') {
            $def = new HTMLPurifier_CSSDefinition();
        } elseif ($type == 'URI') {
            $def = new HTMLPurifier_URIDefinition();
        } else {
            throw new HTMLPurifier_Exception(
                "Definition of $type type not supported"
            );
        }
        $this->definitions[$type] = $def;
        return $def;
    }

    public function maybeGetRawDefinition($name)
    {
        return $this->getDefinition($name, true, true);
    }

    /**
     * @return HTMLPurifier_HTMLDefinition|null
     */
    public function maybeGetRawHTMLDefinition()
    {
        return $this->getDefinition('HTML', true, true);
    }
    
    /**
     * @return HTMLPurifier_CSSDefinition|null
     */
    public function maybeGetRawCSSDefinition()
    {
        return $this->getDefinition('CSS', true, true);
    }
    
    /**
     * @return HTMLPurifier_URIDefinition|null
     */
    public function maybeGetRawURIDefinition()
    {
        return $this->getDefinition('URI', true, true);
    }

    /**
     * Loads configuration values from an array with the following structure:
     * Namespace.Directive => Value
     *
     * @param array $config_array Configuration associative array
     */
    public function loadArray($config_array)
    {
        if ($this->isFinalized('Cannot load directives after finalization')) {
            return;
        }
        foreach ($config_array as $key => $value) {
            $key = str_replace('_', '.', $key);
            if (strpos($key, '.') !== false) {
                $this->set($key, $value);
            } else {
                $namespace = $key;
                $namespace_values = $value;
                foreach ($namespace_values as $directive => $value2) {
                    $this->set($namespace .'.'. $directive, $value2);
                }
            }
        }
    }

    /**
     * Returns a list of array(namespace, directive) for all directives
     * that are allowed in a web-form context as per an allowed
     * namespaces/directives list.
     *
     * @param array $allowed List of allowed namespaces/directives
     * @param HTMLPurifier_ConfigSchema $schema Schema to use, if not global copy
     *
     * @return array
     */
    public static function getAllowedDirectivesForForm($allowed, $schema = null)
    {
        if (!$schema) {
            $schema = HTMLPurifier_ConfigSchema::instance();
        }
        if ($allowed !== true) {
            if (is_string($allowed)) {
                $allowed = array($allowed);
            }
            $allowed_ns = array();
            $allowed_directives = array();
            $blacklisted_directives = array();
            foreach ($allowed as $ns_or_directive) {
                if (strpos($ns_or_directive, '.') !== false) {
                    // directive
                    if ($ns_or_directive[0] == '-') {
                        $blacklisted_directives[substr($ns_or_directive, 1)] = true;
                    } else {
                        $allowed_directives[$ns_or_directive] = true;
                    }
                } else {
                    // namespace
                    $allowed_ns[$ns_or_directive] = true;
                }
            }
        }
        $ret = array();
        foreach ($schema->info as $key => $def) {
            list($ns, $directive) = explode('.', $key, 2);
            if ($allowed !== true) {
                if (isset($blacklisted_directives["$ns.$directive"])) {
                    continue;
                }
                if (!isset($allowed_directives["$ns.$directive"]) && !isset($allowed_ns[$ns])) {
                    continue;
                }
            }
            if (isset($def->isAlias)) {
                continue;
            }
            if ($directive == 'DefinitionID' || $directive == 'DefinitionRev') {
                continue;
            }
            $ret[] = array($ns, $directive);
        }
        return $ret;
    }

    /**
     * Loads configuration values from $_GET/$_POST that were posted
     * via ConfigForm
     *
     * @param array $array $_GET or $_POST array to import
     * @param string|bool $index Index/name that the config variables are in
     * @param array|bool $allowed List of allowed namespaces/directives
     * @param bool $mq_fix Boolean whether or not to enable magic quotes fix
     * @param HTMLPurifier_ConfigSchema $schema Schema to use, if not global copy
     *
     * @return mixed
     */
    public static function loadArrayFromForm($array, $index = false, $allowed = true, $mq_fix = true, $schema = null)
    {
        $ret = HTMLPurifier_Config::prepareArrayFromForm($array, $index, $allowed, $mq_fix, $schema);
        $config = HTMLPurifier_Config::create($ret, $schema);
        return $config;
    }

    /**
     * Merges in configuration values from $_GET/$_POST to object. NOT STATIC.
     *
     * @param array $array $_GET or $_POST array to import
     * @param string|bool $index Index/name that the config variables are in
     * @param array|bool $allowed List of allowed namespaces/directives
     * @param bool $mq_fix Boolean whether or not to enable magic quotes fix
     */
    public function mergeArrayFromForm($array, $index = false, $allowed = true, $mq_fix = true)
    {
         $ret = HTMLPurifier_Config::prepareArrayFromForm($array, $index, $allowed, $mq_fix, $this->def);
         $this->loadArray($ret);
    }

    /**
     * Prepares an array from a form into something usable for the more
     * strict parts of HTMLPurifier_Config
     *
     * @param array $array $_GET or $_POST array to import
     * @param string|bool $index Index/name that the config variables are in
     * @param array|bool $allowed List of allowed namespaces/directives
     * @param bool $mq_fix Boolean whether or not to enable magic quotes fix
     * @param HTMLPurifier_ConfigSchema $schema Schema to use, if not global copy
     *
     * @return array
     */
    public static function prepareArrayFromForm($array, $index = false, $allowed = true, $mq_fix = true, $schema = null)
    {
        if ($index !== false) {
            $array = (isset($array[$index]) && is_array($array[$index])) ? $array[$index] : array();
        }
        $mq = $mq_fix && version_compare(PHP_VERSION, '7.4.0', '<') && function_exists('get_magic_quotes_gpc') && get_magic_quotes_gpc();

        $allowed = HTMLPurifier_Config::getAllowedDirectivesForForm($allowed, $schema);
        $ret = array();
        foreach ($allowed as $key) {
            list($ns, $directive) = $key;
            $skey = "$ns.$directive";
            if (!empty($array["Null_$skey"])) {
                $ret[$ns][$directive] = null;
                continue;
            }
            if (!isset($array[$skey])) {
                continue;
            }
            $value = $mq ? stripslashes($array[$skey]) : $array[$skey];
            $ret[$ns][$directive] = $value;
        }
        return $ret;
    }

    /**
     * Loads configuration values from an ini file
     *
     * @param string $filename Name of ini file
     */
    public function loadIni($filename)
    {
        if ($this->isFinalized('Cannot load directives after finalization')) {
            return;
        }
        $array = parse_ini_file($filename, true);
        $this->loadArray($array);
    }

    /**
     * Checks whether or not the configuration object is finalized.
     *
     * @param string|bool $error String error message, or false for no error
     *
     * @return bool
     */
    public function isFinalized($error = false)
    {
        if ($this->finalized && $error) {
            $this->triggerError($error, E_USER_ERROR);
        }
        return $this->finalized;
    }

    /**
     * Finalizes configuration only if auto finalize is on and not
     * already finalized
     */
    public function autoFinalize()
    {
        if ($this->autoFinalize) {
            $this->finalize();
        } else {
            $this->plist->squash(true);
        }
    }

    /**
     * Finalizes a configuration object, prohibiting further change
     */
    public function finalize()
    {
        $this->finalized = true;
        $this->parser = null;
    }

    /**
     * Produces a nicely formatted error message by supplying the
     * stack frame information OUTSIDE of HTMLPurifier_Config.
     *
     * @param string $msg An error message
     * @param int $no An error number
     */
    protected function triggerError($msg, $no)
    {
        // determine previous stack frame
        $extra = '';
        if ($this->chatty) {
            $trace = debug_backtrace();
            // zip(tail(trace), trace) -- but PHP is not Haskell har har
            for ($i = 0, $c = count($trace); $i < $c - 1; $i++) {
                // XXX this is not correct on some versions of HTML Purifier
                if (isset($trace[$i + 1]['class']) && $trace[$i + 1]['class'] === 'HTMLPurifier_Config') {
                    continue;
                }
                $frame = $trace[$i];
                $extra = " invoked on line {$frame['line']} in file {$frame['file']}";
                break;
            }
        }
        trigger_error($msg . $extra, $no);
    }

    /**
     * Returns a serialized form of the configuration object that can
     * be reconstituted.
     *
     * @return string
     */
    public function serialize()
    {
        $this->getDefinition('HTML');
        $this->getDefinition('CSS');
        $this->getDefinition('URI');
        return serialize($this);
    }

}

// vim: et sw=4 sts=4