public function parse($str = null, $initialVariables = null)
    {
        if (is_array($str)) {
            $initialVariables = $str;
            $str = null;
        }

        $oldVars = $this->registeredVars;
        if ($initialVariables !== null) {
            $this->setVariables($initialVariables);
        }

        if ($str == null) {
            if (empty($this->_parseFile)) {
                throw new exception('nothing to parse');
            }

            $out = $this->compileFile($this->_parseFile);
        } else {
            $out = $this->compile($str);
        }

        $this->registeredVars = $oldVars;

        return $out;
    }