@classmethod
def from_label(cls, group_field_xml):
    """ Initializes the meta data from an XML description of the Group_Field.

        Parameters
        ----------
        group_field_xml : Label or ElementTree Element
            Portion of the label describing this group field.

        Returns
        -------
        Meta_Group
            Contains meta data for Group_Field_* fields.
        """
    obj = cls()
    obj._load_keys_from_xml(group_field_xml, tag_modify=('group_', ''))
    keys_must_exist = ['repetitions', 'fields', 'groups']
    if 'Delimited' not in group_field_xml.tag:
        keys_must_exist.extend(['location', 'length'])
    obj._check_keys_exist(keys_must_exist)
    return obj
