'Return the string to use as the ``__doc__`` attribute of the property
for this attribute.'

@property
def _docstring(self):

    return ('%s    type-converted    value    of    ``%s``    attribute,    or    |None|    (or    specified    default    value)    if    not    present.    Assigning    the    default    value    causes    the    attribute    to    be    removed    from    the    element.' % (self._simple_type.__name__, self._attr_name))
