private function _getRequiredVars( $template_identifier )
	{
		if ( !( isset( $this->_available_templates[$template_identifier] ) ) )
		{
			trigger_error( "Template identifier not found.", E_USER_ERROR );
		}

		$template_path = ROOT_PATH.'/'.$this->_available_templates[$template_identifier];

		if ( !( $template_source = file_get_contents( $template_path ) ) )
		{
			trigger_error( "{$template_path} not found.", E_USER_ERROR );
		}

		if ( !( preg_match_all( '/{.*\$([a-z_\-]*).*}/', $template_source, $matchs) ) )
		{
			trigger_error( "Not found in use vars in the tpl source.", E_USER_WARNING );
		}

		$required_vars = array_unique( $matchs[1] );

		// Remove url.
		unset( $required_vars[array_search( 'url', $required_vars )] );

		return $required_vars;
	}