Well, it kinda depends on what you mean by "plain text" and what you mean by "support." You can get a lot of these things through text-markup systems like Markdown.
There's a growing class of editors that strive to provide a richer document experience while still relying on plain text as the file format. I don't usually suggest normal people adopt it, but an example of this kind of hybrid approach is Orgmode in emacs. I can do ALL SORTS OF THINGS with my org files, but the actual data is still just plaintext with minimal and human-readable markup. The editor does the rest of the work.
If you mean "it's technically text but you have to have a program that knows how to parse it" then it's not really much of an advantage over docx having zipped XML.
There was an (astute, I think) article from "Joel on Software" years ago saying that the main reason that supporting the Word format was hard was that, by implication, you needed to implement every feature Word had to do it right.
> it's not really much of an advantage over docx having zipped XML.
a plain-text light-markup file -- easily read, parsed, and rewritten when necessary by a plethora of apps (text-editors, spell-checkers, grammar-checkers, link-checkers, sanitizers, validators, on and on) -- is a big advantage (gargantuan!) over a complex xml-format document stored in a .zip container.
and editing and ease-of-use (and re-use and repurposability) is much friendlier as well.
light-markup will never do everything ms-word does.
nor should it.
but typical light-markup systems these days handle
all of the features needed for the vast majority of
long-form documents which are now being produced --
books, annual reports, scientific articles, etc. --
and do it with an eye toward mounting on the web.
whereas ms-word is still stuck in a page mentality,
and creates .html output which is rather horrendous.
but i agree that ms-word is still valuable to many.
and i no longer feel it necessary to bludgeon word
for being the "de facto default" out in the world,
where everybody uses it because everybody uses it,
and nobody can use anything else because "conform".
so if someone needs one of the "does more" things
where ms-word does more, i'm glad they have word.
it's a tool in their chest, no reason to begrudge.
i'm happy, even, that word has true fans like you.
i'm also glad the rest of us can move on now to
something that we think is better. it's about time.
The examples I'd hold up as useful here keep the markup simple, so that the files are still usable when viewed directly, but provide lots of other functions by being clever.
Again, Orgmode is a great example. I can (and sometimes do) use my org files outside of emacs.
There's a growing class of editors that strive to provide a richer document experience while still relying on plain text as the file format. I don't usually suggest normal people adopt it, but an example of this kind of hybrid approach is Orgmode in emacs. I can do ALL SORTS OF THINGS with my org files, but the actual data is still just plaintext with minimal and human-readable markup. The editor does the rest of the work.
I find that promising.