[egeimicu] editing Emacs Lisp

consider editing code with an editor, a very common activity.

transformations to code, editing it, or even just navigating it, can be arbitrarily complex (e.g., jump from function use to function definition), so we want a computer programming language to be able to express and implement the possibilities.  many IDEs are extendable with an embedded language, famously Emacs.  then, we want to do arbitrarily complex edit operations on that embedded editing code, again wanting a programming language to express and implement those operations.  the need for programming languages to edit programming languages continues recursively, infinitely.

Emacs is pretty good for editing Emacs Lisp.  for example M-x apropos sexp lists many functions (and other things) for manipulating s-expressions.

previously, listing some of the possible editing actions.