[$] An alternate pattern-matching conditional for Elisp

One of the outcomes of the (extremely) lengthy discussion about usingCommon Lisp features in Emacs Lisp (Elisp), which we looked at back in November, was an effort tostart removing some of those uses from Emacs. The rewrite of some of theElisp in Emacs that uses the Common Lisp library (cl-lib) was started byRichard Stallman as a way to reduce the cognitive load needed formaintaining Emacs itself. Since then, he has broadened his efforts tosimplify Elisp by adding a new pattern-matchingconditional that would be a competitor to pcase,which is a longstanding macro that he finds overly complex.