def _String(parser, propObj, propCls, propName, propHelp, shortArg, longArg,
    atype=str):
    """Adds an argument to the given parser for the given :class:`.String`
    property.

    :param parser:   An ``ArgumentParser`` instance.

    :param propCls:  A ``HasProperties`` class or instance.

    :param propObj:  The ``PropertyBase`` class.

    :param propName: Name of the property.

    :param propHelp: Custom help text for the property.

    :param shortArg: String to use as the short argument.

    :param longArg:  String to use as the long argument.

    :param atype:    Data type to expect (defaults to ``str``). This allows
                     the conversion type to be overridden for some, but not
                     all, property types.
    """
    parser.add_argument(shortArg, longArg, help=propHelp, type=atype)
