Parse the root XML element as an array.

def parse_at_root(
            self,
            root,  # type: ET.Element
            state  # type: _ProcessorState
    ):
        # type: (...) -> Any
        """Parse the root XML element as an array."""
        if not self._nested:
            raise InvalidRootProcessor('Non-nested array "{}" cannot be root element'.format(
                self.alias))

        parsed_array = []  # type: List

        array_element = _element_find_from_root(root, self._nested)
        if array_element is not None:
            parsed_array = self.parse_at_element(array_element, state)
        elif self.required:
            raise MissingValue('Missing required array at root: "{}"'.format(self._nested))

        return parsed_array