Identifiers are used for naming objects of data, labels and switches, procedures, macros and their formal parameters. An identifier consists of an arbitrary sequence of lower case letters and digits, starting with a letter. It carries no information in its form, e.g. single-letter identifiers are not reserved for special purposes. It may be of any length, though it is permissible for compilers to disregard all but the first twelve printing characters. As layout characters are ignored, spaces may be used in identifiers without acting as terminators.
Id ::=
Letter
Letterdigitstring
Letterdigitstring ::=
Letter
Letterdigitstring
Digit
Letterdigitstring
Void
Letter ::= a b c d e f g h i j k l m n o p q r s t u v w x y z
Digit ::= 0 1 2 3 4 5 6 7 8 9
An obvious liberty is taken with the layout of alternatives in the above rules.