Identifiers and Reserved Words ☆☆
Identifiers
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.
(Note)
User-defined function names need not start with FN.
The maximum length of identifiers is 31 in the standard.
When Option-Compatibility-Identifier characters-include Greek is checked, Greek characters can be used for identifiers.

Reserved Words
The following words are prohibited to be used as identifiers by the standard.
`PI,RND,MAXNUM,DATE,TIME,EXLINE,EXTYPE,CON,IDN,ZER,
TRANSFORM, NOT,ELSE,PRINT,REM, DATE$,NUL$,TIME$
` (Note.)
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.