Identifiers denote programmer defined names for specific constants, types, variables, procedures and functions, units, and programs. All programmer defined names in the source code – excluding reserved words – are designated as identifiers.
Identifiers consist of between 1 and 127 significant characters (letters, digits and the underscore character), of which the first must be a letter (a–z or A–Z), or an underscore (_). The following diagram gives the basic syntax for identifiers.
Like Pascal reserved words, identifiers are case insensitive, that is, both
refer to the same procedure.
Remark As of version 2.5.1 it is possible to specify a reserved word as an identifier by prepending it with an ampersand (&). This means that the following is possible:
program testdo; procedure &do; begin end; begin &do; end.
The reserved word do is used as an identifier for the declaration as well as the invocation of the procedure do.