ies, 'y' is omitted. 
 NOTE: x and y are the first two arguments. All other arguments require
        the 'name',value notation.

    'weights' Prior weights for observations (reciprocal of variance, or
           sample size). 
    'cens' Censoring indicators for hazard rate or censored regression.
           The coding is '1' (or 'TRUE') for a censored observation, and
           '0' (or 'FALSE') for uncensored observations. 
    'base' Baseline parameter estimate. If a baseline is provided,
   