We need to consider having defaults or "internal options" that aren't exposed on the options object because we often sync those options with the data attributes on the dom element.
[popup] Move non-option constants to defaults object -- Helps fix #4974
OK, so "fix #nnnn" is also a magic sequence ... noted ...
There's a Google doc that lists all the options.
I think after the widget review we've settled this whole options business.