fairly early in PDP-11 development ed gained three
features: & in the
rhs of substitutions plus k and t commands. (I'm not sure about & ....
Oh, and backreferencing, which took regular expressions way up the
complexity hierarchy--into NP-complete territory were it not for the limit
of 9 backreferenced substrings. (Proof hint: reduce the knapsack problem to
an ed regex.)
Also g and s were generalized to allow escaped newlines.
I was indeed wrong about &. It was in v1.
Doug