In this example, there exists an editable text widget field as follows:
quantity: [______]
Adding certain custom text-properties -- 'overwrite t -- to the underscores between the square-brackets ______ seems to be the first step.
How can a user enable overwrite typing within the confines of the square brackets, based upon the the existence of certain custom text-properties?
There are some packages that do similar things -- however, none that are based on text properties.
In org-mode you can edit table fields, while the tables themselves stay in place.
In my package dynamic-spaces any sequence of two or more spaces are seen as "dynamic" so you could, for example, edit code while end-of-line comments stay in place.
Side comment: I don't think "overwrite" is what you are looking for. If there already is text in the box, you would like the editing to be normal. Concretely, if the box contains "5" and the point is before the 5 and you type "1", you would like to get "15", not "1".
