Identifiers (also referred to as names) are described by the following lexical definitions:
identifier | ::= | (letter|"_") (letter | digit | "_")* |
letter | ::= | lowercase | uppercase |
lowercase | ::= | "a"..."z" |
uppercase | ::= | "A"..."Z" |
digit | ::= | "0"..."9" |
Identifiers are unlimited in length. Case is significant.