selection standard variable doesn't include form fields

[neocotic]

A user has raised a bug stating that {selection} did not include form fields. I didn't originally consider this use case when I originally added this feature but it is something that I'd like to add support for, however, I can imagine it being tricky as I'm not sure of the optimal way of checking this in the DOM, which could potentially contain a lot of text fields which would each have to be checked for selected text.

I'm going to mark this as a feature request for now since I don't see it as a bug with {selection}, but an extension of it.