Thank you. Some additional clues: the jargon file started at SAIL, and shortly after was adopted by MIT and then jointly maintained. So it's
not clear which one is "the PDP-6" here. As far as I know, Bill Weiher, the creator of STOPGAP and/or SOS?, is associated with SAIL, not MIT.
You are welcome. I'm sorry to confuse the origin and the historical correction. I was using the docs I had, and as you pointed out, the Jargon says PDP-6 but does not specify which site. My notes from the later PDP-10 pointed at DEC+MIT. It does sound like STOPGAP/SOS came to the DEC world from Stanford. So thank you.
That said, bring it back to the original question from Will. My original email was about the history of using reg-ex WRT to UNIX. It was less about editors and who did what as much as trying to point out that the idea of a text editor existed long before Ken's version of QED, much less, ed(1). Most importantly, Ken's QED came after the original QED, which came after other text editors. Adding reg-ex to an editor was natural for someone schooled in the ideas behind automaton and pattern matching. But tmany/most of the text editors in used had been created before that work had begun to be studied and formalized, so, these other editors had not included using reg-ex for the pattern match/search scheme.
Ken's great leap was modeling and combining the QED user interface with this new idea in text pattern match/searching, demonstrating that it was a good fit. That would lead to other tools that decided to include the same pattern-matching ideas (grep, sed, awk, Perl, et al.).
Will had asked -- how did people learn to use reg-ex? The observation I had made and was bringing forward to the list is that if new user came from a background based on being taught about how to create a pattern match er, and sid person had learned a little about the ideas behind automatons, learn to use reg-ex was not a big deal. It was only 'astonishing,' and users might need a separate explanation if they started from some other place - particularly if they did not have that same background in core CS theory/they had previously learned a different way with a different set of tools, such as the text editor.
As I understand it, this is how Will came to learn UNIX, so folks like Will needed and appreciated documentation that came from other places. I think that he was asking which documents and what people in the background similar to him had chosen to use to learn how to use the UNIX toolkit.