HTMLPurifier_Config::set PHP Method

    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;
    }

 private function setConfigAttribute(HTMLPurifier_Config $config, $key, $subkey, $value)
 {
     if (version_compare($config->version, '4.0.0') >= 0) {
         $config->set("{$key}.{$subkey}", $value);
     } else {
         $config->set($key, $subkey, $value);
     }
 }