public function usingCallback(string $name, $instance): self
    {
        $this->xslCallbacks->addCallback($name, $instance);
        return $this;
    }
public function usingCallback(string $name, $instance): self
    {
        $this->xslCallbacks->addCallback($name, $instance);
        return $this;
    }
public function usingCallback ( string $ name , $ instance ) : self { $ this -> xslCallbacks -> addCallback ( $ name , $ instance ) ; return $ this ; }
register an instance as callback

@param   string  $name      name to register the callback under
@param   object  $instance  the instance to register as callback
@return  \stubbles\xml\xsl\XslProcessor
register an instance as callback