This is similar in spirit to the request to document the flags generated by measurement algorithms. As such, I'm assigning it to team SQuaRE and linking it to DM-6887 & DM-6655 in the hope that Jonathan Sick & colleagues will give us a steer about how best to approach it. Ultimately, though, I expect afw-side implementation and actually writing the docs may be a Pipelines deliverable.

On the subject of mask planes, I note the Jim Bosch comment on Slack of 2018-02-05:

It now effectively means "this pixel was interpolated in one of the inputs and that's okay because we think the interpolation was good...

I think that's actually what `interpolated` was always supposed to mean, actually, but there were bugs in how we set INTRP and SAT in ISR that made it safest to flag on whether a pixel was interpolated rather than why it was interpolated. There should now always be an additional "why" flag set whenever INTRP is, and we should prefer to do filtering on those. For example, we're much better at interpolating CRs (can usually be trusted) than saturation (generally cannot).

This seems like something that should be included in the new documentation.

Sounds good. Yes, step 1 is figuring out where to integrate the docs with the code, and then how to pull that information out usefully.

This will require some back-and-forth:

• Science Pipelines needs to add a place in the Mask object where documentation can go.
• Science Pipelines needs to actually put documentation there.
• SQuaRE needs to write something to extract those docstrings and put them in the HTML.

The third step is conceptually similar to the problem documentation for pex_config objects.  I'll go create a new ticket for Science Pipelines to tackle the first two steps, so we can use this one for the third.