2.3.3. - Identifiers
An identifier is a name -- it can be a variable name, a macro name or an array name. An identifier may begin with the letters
a-z, A-Z or
_ (underscore).
The remaining letters in a name may be those characters
or the digits
0-9. There is no limit to the number of characters in a variable name.
In the syntax rules described later, such names are represented by
the term
identifier.