This reminds me of how Nisus (the word processor program) styled text. The document, a Classic-Mac-OS file, contained plain text in the data fork and styling information in the resource fork. If I recall correctly!
Yes, this was a rather good way to deal with it. Even if the content wasn't rich text, it still may have things like current position, folded sections and so on. It totally pays to keep this stuff separate from the main content as the latter stays readable by any other program that supports text.
In general the whole business of file type plus creator type felt much better than the single file type of now. E.g. in desktop publishing Illustrator EPS were very different from Photoshop EPS and it was very convenient to be able to tell them apart.
In general the whole business of file type plus creator type felt much better than the single file type of now. E.g. in desktop publishing Illustrator EPS were very different from Photoshop EPS and it was very convenient to be able to tell them apart.