#NEWLINE# @ classmethod #NEWLINE# def add_field( cls , field_cls ) : #NEWLINE# #INDENT# 'Adds a field class to this fieldset.\n\n        The field will be rendered inside this fieldset on the page.\n\n        A given field class can only be in one fieldset. Its ``field_id``\n        must be unique.\n        ' #NEWLINE# field_registry . register ( field_cls ) #NEWLINE# cls . field_classes . append ( field_cls )