Amiga had datatypes.library, and also IFF filetypes (that were mostly lovely) designed be EA for DPaint. It's the way the world should work.

Let's say you're MS writing word for the Amiga.

They provide a datatypes description for doc files. this gives ability to read and write the format, and fingerprint it (not based on extension).

Now any program, old or new, that wants to read or write doc files can do. It's just there.