@craigbro @tomjennings @davefischer
> what was the maintenance work
That's a really good question actually. I'm not sure if I can remember specifically, although I do know that there are new versions of things released from time to time. I think it was mostly pressure from users to fix bugs or add features.
TECO was remarkably stable as I recall, Vastly more so than Emacs lisp, which completely wrecks my extensions every single time there's a new major version. And with small exceptions, people mostly did not call other libraries as subroutines. They just built their libraries directly on TECO.
It's possible that ZBabyl, my library for Zmail compatibility on top of the Babyl malil reader made some assumptions about Babyl, but probably those were not violated very often, if at all.
I'm not saying the tenor of the time was that there was no software rot. Maclisp used to change incompatibly almost every week, and this is one of several pressures that led to Common Lisp. There is a tension between the need to develop new things and the need to be stable so that new things can be layered on top.
TECO may have had small things added to it, but I don't perceive that it changed a lot. At least I don't remember it impacting me much.
And the operating system did change but generally in compatible ways, not withstanding the dire nature of a name like incompatible time sharing system. That was mostly a name joke about CTSS (the compatible time sharing system) as I was told, though never bothered to check.
For example I think I mentioned some recent message about the echoin system call being added to the OS. TECO and/or emacs advantage of that, but I don't think it affected most programs, including most emacs libraries.
So I'm going to go out on a limb on the basis of far too little information, since I only maintained a few libraries, and say that most of it was just feature requests and in-library bug fixes in a time when it was popular to be very responsive to such things in order to maintain a customer base.
I wrote TeX mode. I think there was a trivial one before that, but I'd found it to trivial to use. As I recall it's concept of what a dollar sign was was just a variant of vertical bar in lisp, which was really inadequate. Mine added things like flashing matching dollar signs and separate managing of bracketing enclosure differently inside of dollar signs and outside. I was doing a lot of editing in a raw TeX and needed unbalanced things to work well. It had support for looking at things in comments that you could leave to say to view the buffer as different zones of correctness so that one type of graphical and completeness somewhere didn't poison the whole buffer's syntax analysis.
I hope/think the stuff I did on this got transliterated into emacs-lisp code.
I wrote a version of lisp mode that extended indentation to work like the list machine where it knew that some number of forms have special indentation before the body. This data driven so you could declare your own operators to have that same concept. I suspect somebody transliterated this as well to emacs-lisp.
And I wrote a mode line manager MODLIN, that my NEX library (an extension of Bob Kerns' EX library, which was partly borrowed from Lunar and other libraries). There was a lot of redundancy and not all of those libraries needed to survive.
NEX had a nice feature, which Jonathan Rees might have imported into gnex, I have not checked, of flashing the matching backquote when you type a comma in lisp mode. That was a case where an extension was needed because backquote was not originally in Lisp. And c-x # for keyboard macros arose just because I had a lot of things that were numbered and I wanted the keyboard macro to be able to insert successive numbers.
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