[Numpy-discussion] Default value in documentation

[Pierre GM]

All,
I'm starting to update the documentation of maskedarray to the latest 
standard.
How should I represent the default value of an optional parameter ?
I was thinking something like

def function(a, value=None)
    """Does something
*Parameters*:
    a : {ndarray}
        Input array.
    value : {float} *[None]*
        Some value. If None, a default based on the dtype of a is used.
    """"

Suggestions/ideas are welcome.
Thanks a lot in advance
P.