public function withAppended(Element $el): self
    {
        $obj = clone $this;
        array_push($obj->_elements, $el);
        return $obj;
    }
public function withAppended(Element $el): self
    {
        $obj = clone $this;
        array_push($obj->_elements, $el);
        return $obj;
    }
public function withAppended ( Element $ el ) : self { $ obj = clone $ this ; array_push ( $ obj -> _elements , $ el ) ; return $ obj ; }
Get self with an element appended to the end.

@param Element $el Element to insert into the structure
@return self
Get self with an element appended to the end .