function extend($tag,$func) {
		$this->tags.='|'.$tag;
		$this->custom['_'.$tag]=$func;
	}
function extend($tag,$func) {
		$this->tags.='|'.$tag;
		$this->custom['_'.$tag]=$func;
	}
function extend ( $ tag , $ func ) { $ this -> tags .= '|' . $ tag ; $ this -> custom [ '_' . $ tag ] = $ func ; }
Extend template with custom tag
@return NULL
@param $tag string
@param $func callback
Extend template with custom tag