Identifiers are used for define names, variable names, array names, and function names.

Identifiers must start with an alphabetic character or underscore ('_') character, and may be following be any number of alphanumeric characters or underscore.

These are all valid identifiers:

Indentifiers are not case sensitive.

For example, 'Test', 'TEST' and 'test' are all the same identifiers.

However, it is allowed for identifiers to be reused for functions.