Hi Leo and George,

I've taken a stab at improving the "Substitutes" section.  Please let me
know if you have any concerns by replying to the patch email submission:

https://debbugs.gnu.org/cgi/bugreport.cgi?bug=29271

I think the existence of this email thread proves that the question of
"Are substitutes enabled by default?" does not have an obvious answer.
I also think that the existence of this email proves that the behavior
of the --fallback command is not obvious, so it requires a very careful
explanation in the manual to eliminate any risk of misinterpretation.

Please do not reply to this email with feedback on the patch series;
please respond to the patch email if you have feedback on the patch.

-- 
Chris