Support full strings for ID3 track number (TRCK)

The ID3v2.4 native frames standard states the following for the track frame:

The 'Track number/Position in set' frame is a numeric string [...]

and the following in the main structure standard:

A numeric string is a string that consists of the characters "0123456789" only.

In my non-standard collection, some tracks have vinyl-like track numbering: "A1", "A2", "B1", "B2" and so forth.

In rekordbox, all these track numbers appear as "0".

Even though it's not in the ID3 standard, it would be nice if rekordbox would support strings for the track number frame.