Language Basics
Naming
Variable names are case-sensitive.
A variable's name can be any legal identifier —
an unlimited-length sequence of Unicode letters
and digits, beginning with a letter, the dollar sign
"$", or the underscore character "_".
The convention, however, is to always begin your
variable names with a letter, not "$" or "_".
Additionally, the dollar sign character, by
convention, is never used at all.