Aaron Ecay wrote:
> I was surprised to learn that this is the case, in light of what is
> said in the Elisp reference about symbol names

Good point; thanks. In the spirit of "be strict about what you generate", the 
Emacs printer should escape any character that is not in the list of characters 
documented in the Elisp manual as being safe (i.e., as not requiring escaping). 
This is elementary future-proofing, and is independent of whether we want Emacs 
to warn about or disallow confusable chars in symbols.

Proposed patches against 'master' attached. The first merely simplifes the code 
without changing its effect. The second fixes a bug in the manual, which 
incorrectly states that '?' never needs escaping in symbol names. These two 
patches are routine. (I assume the second one should be applied to emacs26 
instead of to master.)

The third patch changes the Lisp printer to escape characters as suggested above.

The fourth patch changes the Lisp printer to escape '?' only at the start of a 
symbol. This is nicer for programs using Scheme-style naming conventions in 
Emacs Lisp, e.g., 'fooish?' rather than 'fooishp'. I discovered the need for 
this patch when I wrote the second patch.