@classmethod
def from_label(cls, xml_header):
    """ Create a Meta_HeaderStructure from the XML portion describing it in the label.

        Parameters
        ----------
        xml_header : Label or ElementTree Element
            Portion of label that defines the Header data structure.

        Returns
        -------
        Meta_HeaderStructure
            Instance containing meta data about the header structure, as taken from the XML label.

        Raises
        ------
        PDS4StandardsException
            Raised if required meta data is absent.
        """
    obj = cls()
    obj._load_keys_from_xml(xml_header)
    keys_must_exist = ['object_length', 'offset', 'parsing_standard_id']
    obj._check_keys_exist(keys_must_exist)
    return obj
