Selects an item by the text content of the child.

        Args:
            value (str): Text content of the item that have to be selected.

def select_by_value(self, value):
        """Selects an item by the text content of the child.

        Args:
            value (str): Text content of the item that have to be selected.
        """
        self._selected_key = None
        self._selected_item = None
        for k in self.children:
            item = self.children[k]
            item.attributes['selected'] = False
            if value == item.get_value():
                self._selected_key = k
                self._selected_item = item
                self._selected_item.attributes['selected'] = True