Identifiers and Reserved Words ☆☆

Identifiers are the name of variables, functions or subprograms.
An Identifier is an alphabet or an alphabet succeeded by alphabets, numerals or underscores.
A string identifier ends with $.
Identifiers of BASIC are case-insensitive. For example, 'A' and 'a' are identical.
Underscores can be included as angle_A.
User-defined function names need not start with FN.
The maximum length of identifiers is 31 in the standard.

Reserved Words
The following words are prohibited to be used as identifiers by the standard.
Any word except the above can be used as a name of any variable or function.
For example, a user can define a function whose name is identical with a supplied function.