Icon Text Drag and Drop queries

Recent versions of RO5 implement Drag&Drop for selected text in Writable icons, whether the selection be the whole text or partial. This is an excellent and long-awaited facility.

The only documentary reference I can find for this facility is in the original (from 2015!) Drag-And-Drop Functional Spec). The new Style Guide also has details of how Drag&Drop and Cut&Paste should work.

The D&D Spec implies in the section on Draggable-Writable Icons that for the Wimp to perform partial or complete selects of icons, or drags of selections, the icons must be defined as Writable, and not Writable/Drag – which was not immedately obvious to me!

I have been investigating why an application does not enable selecting & dragging part of a writable icon, and have found that it is because the icon is defined with an Button Type of 14 (Writable/Drag) rather than 15 (Writable). The application has implemented drag to copy the whole icon text for many years, and so needs 14 to work, as 15 does not return clicks.

In RO4.39 Writable icons can be selected, but do not drag.
In RO5.24 (and earlier) Writable icons cannot be selected or dragged.
In RO5.28 and later, Writable seems to work fine for selecting & dragging all or part of the icon contents.

For all versions, Writable/Drag icons works fine for dragging the whole text, using the app code, but it would be better to use the standard D&D facility if available.

Before I start investigating changing the 60+ icons in the app which are defined as Writable/Drag to Writable, in a way that dragging icon text still works with RISC OS RO4 and later, I have some questions:

1. Are there any better references available?
2. If D&D is available, do I have to dynamically change all affected icons from button type 14 to 15 to cater for all RO versions?
3. How do I detect that D&D is available?
4. Are there any modules that ould affect this process?