Set ``Attr`` object in this collection.

def setNamedItem(self, item: Attr) -> None:
        """Set ``Attr`` object in this collection."""
        from wdom.web_node import WdomElement
        if not isinstance(item, Attr):
            raise TypeError('item must be an instance of Attr')
        if isinstance(self._owner, WdomElement):
            self._owner.js_exec('setAttribute', item.name,  # type: ignore
                                item.value)
        self._dict[item.name] = item
        item._owner = self._owner