How to determine “Checked” value for Checkboxes (from GetAppearanceStates)

Question

I have a question about checkbox fields, and consistently figuring out which value to use for a checked state.

I have been searching, and shelled out $50 for th

Answer 1

ISO 32000-1:2008 ("PDF 1.7 spec") says in 12.7.4.2.3 ("Check Boxes"):

The appearance for the off state is optional but, if present, shall be stored in the appearance dictionary under the name Off. Yes should be used as the name for the on state.

So if there's an appearance for the unchecked state, it has to be Off. The Yes for the checked state is a recommendation; it can be named differently.

If 2 arbitrary names are used for checked and unchecked, you can't reliably determine which should be used for checked and which for unchecked.