RE: [External] : PATCH: Explicitly show how let works on global-variables

[Drew Adams]

This isn't quite correct:

     When you use a system-wide variable in
     @code{let}, its value is modified in its
     scope and then restored.

1. I'm guessing that by "system-wide" (which is not
   defined) you mean a "special", i.e., "dynamic" var.

2. Dynamic binding has no notion of scope, actually.
   It's instead about duration: the binding has dynamic
   _extent_: it remains in effect until the `let' is
   finished.

See CLTL2, section "Scope and Extent": 
https://www.cs.cmu.edu/Groups/AI/html/cltl/clm/node43.html

("The term 'dynamic scope' is a misnomer. Nevertheless
it is both traditional and useful.")