Visit and execute a operation in element and descendants.

        :param element: The element.
        :type element: hatemile.util.html.htmldomelement.HTMLDOMElement
        :param operation: The operation to be executed.
        :type operation: function

def _visit(self, element, operation):
        """
        Visit and execute a operation in element and descendants.

        :param element: The element.
        :type element: hatemile.util.html.htmldomelement.HTMLDOMElement
        :param operation: The operation to be executed.
        :type operation: function
        """

        if self._is_valid_inherit_element(element):
            if element.has_children_elements():
                children = element.get_children_elements()
                for child in children:
                    self._visit(child, operation)
            elif self._is_valid_element(element):
                operation(element)