How to determine the types of interactive form fields

Question

Hello:
I have written a utility that traverses through the objects in a PDF file, and finds the ones of Type "Annot", Subtype "Widget". I need to go one step down the hierarchy and determine which kind of widget (text, radio button, check mark, press button) is the one under scrutiny.
I have looked at the innards of PDF files, and found that the widgets of type "text" are internally identified by the FT=Tx dictionary entry. So far, so good.
Here is where the beauty and consistency stops. It turns out that all the other (non-text) types are ambiguously identified by FT=Btn dictionary entry.
So: Every field which is not text, is a button.
Where should I look?
TIA,
-RFH

Answer 1

Digging a little deeper, I found that the 4 types of fields (as generated by default) have different keys, as follows:
Text: [F, FT, MK, P, Rect, Subtype, T, Type]
Check Box: [AP, AS, F, FT, MK, P, Rect, Subtype, T, Type]
Radio Button: [AP, AS, BS, F, FT, Ff, MK, P, Rect, Subtype, T, Type]
Button: [AP, DA, F, FT, Ff, MK, P, Rect, Subtype, T, Type]
Is that the correct approach to determine the kind of fields, by querying for the keys, which somehow instantiate a fingerprint?
TIA,
-RFH