JJ Johson, it's not about defintions. But being speaking creatures, we have to use words, right? You can call them Paul and Peter if you prefer that. I was just distinguishing between standard fields (shipped with MP3Tag) AND fields created by the user individually, i.e. "my-super-additional-user-field". ok?
My point was that if a user deletes a vital field, such as "title" or "album" (or any other standard field), there is no way to bring it back, as there is no undelete function (I am refering to the FIELD NAMES, not FIELD CONTENT!). Hence my idea of a pop-up warning before a standard field would be deleted.
However I have just figured out -- thanks to Detlev's posting above -- that there already is a way to reset the list (i.e. to resurrect any possibly deleted standard field names).
So seeing this new situation, I am actually satisfied personally. So the RFE might be cancelled.
However I do still think that a pop-up message before deleting any field name would make sense.
Because it is a safety measure against accidental deletions.
And I don't think deleting field names happens so often that a pop-up message would be annoying.
In case it could be construed as being considered annoying, there would still be the possibility to add a checkbox "don't show warning again".