public function addDirectiveHandler($key, callable $callback = null)
    {
        if (!array_key_exists($key, $this->directiveHandlers)) {
            $this->directiveHandlers[$key] = $callback;
        }
    }
public function addDirectiveHandler($key, callable $callback = null)
    {
        if (!array_key_exists($key, $this->directiveHandlers)) {
            $this->directiveHandlers[$key] = $callback;
        }
    }
public function addDirectiveHandler ( $ key , callable $ callback = null ) { if ( ! array_key_exists ( $ key , $ this -> directiveHandlers ) ) { $ this -> directiveHandlers [ $ key ] = $ callback ; } }
Adds a handler for the named directive.

@param string        $key
@param callable|null $callback
Adds a handler for the named directive .