Parse the given element as the root of the document.

def parse_at_root(
            self,
            root,  # type: ET.Element
            state  # type: _ProcessorState
    ):
        # type: (...) -> Any
        """Parse the given element as the root of the document."""
        xml_value = self._processor.parse_at_root(root, state)
        return _hooks_apply_after_parse(self._hooks, state, xml_value)