In this respect, I think an excellent place to start might be
something you are planning already anyway: update the user documentation
I would include tests as well. Rather than hammer out a full standard based on extensive discussions and negotiations, I would suggest NumPy might be able set a de-facto "standard" based on pieces of the the current numpy user documentation and test suite.
I think this is potentially useful, but *far* more prescriptive and detailed than I had in mind. Both you and Nathaniel seem to have not understood what I mean by "out of scope", so I think that's my fault in not being explicit enough. I *do not* want to prescribe behavior. Instead, a simple yes/no for each function in numpy and method on ndarray.
I quite like the idea of trying to be better at defining the API through tests - the substitution principle in action! Systematically applying tests to both ndarray and MaskedArray might be a start internally (just a pytest fixture away...). But definitely start with more of an overview. -- Marten