What are the new rules for variable scoping in Emacs 24?

Question

Emacs 24 now has lexically-scoped variables. It also still has dynamically-scoped variables, of course. Now that it has both, I\'m quite confused about when a variable will have

Answer 1

The manual is the definitive source. Start here:

C-hig (elisp) Variable Scoping RET

I had originally quoted the manual in this answer, but that information (dating back to Emacs 24.0.90.1) was slightly out of date. Better to read the manual from inside Emacs so that the information will be correct for the version you're using.

If you particularly want to read it on a web page, the current version is:
http://www.gnu.org/software/emacs/manual/html_node/elisp/Variable-Scoping.html