standard file extensions for exported apple dos files ?

[Jonno Downes <jonnosan@gmail.com>]

howdy,

I'm playing with some code where it will be handy for me to have on a
modern file system (e.g. ntfs) some files exported from Apple DOS 3.3
disk images, but I'd like to retain the 'file type' metadata when I do
that.

More specifically, I want to recognise 1) that the files are Apple 2
files, and 2) differentiate between Binary files (with the first 4
bytes being load address and file length), Applesoft files, Text files
etc.

The only cross-platform place for storing file metadata is in the file
extension, but there doesn't seem to be any convention or standard
file extension used for this purpose - BIN and BAS are too generic.

I am considering using .?33, where the first char is the DOS 3.3 file
type (i.e. a binary file will get saved with extension .B33, an
Applesoft file will get .A33 etc).

But is anyone aware of unique extensions already being used for this
purpose?