MAJOR BUG (mode lines)

[Mark Horton]

Why do you assume this is a bug?  It was put in as a feature at the
request of some users, so that vi "set" commands could automatically
be run when certain files are entered.  EMACS has a similar feature.
The only problems are (1) it isn't documented (an oversight on my part),
and (2) you seem to have found a security problem.  It would indeed be
possible to take the feature out (and since most of you didn't know it
was there, you'd never notice that it was gone), but it makes more sense
to set a flag while checkmodeline is in operation, and refuse to do
any ! or sh commands with this flag set.

The mode line feature was put into vi version 3.7, and is still in, so
it's in 4.2BSD and System V.