'*nonpos*: [\'mask\' | \'clip\' ]
values beyond ]0, 1[ can be masked as invalid, or clipped to a number
very close to 0 or 1'

def __init__(self, axis, nonpos=u'mask'):

    if (nonpos not in [u'mask', u'clip']):
        raise ValueError(u"nonposx,    nonposy    kwarg    must    be    'mask'    or    'clip'")
    self._transform = LogitTransform(nonpos)
