Identifiers

An identifier is a series of characters that are not contained in a comment or a constant.

Except for P, PIC, and PICTURE, identifiers must be preceded and followed by a delimiter. (P, PIC, and PICTURE identifiers can be followed by a character string.) The first character of an identifier must be an alphabetic or extralingual character. If the identifier names an INTERNAL symbol, it can also use the break (_) character as its first character. Other characters, if any, can be alphabetic, extralingual, digit, or the break (_) character. External user names must not start with IBM, PLI, CEE, _IBM, _PLI, and _CEE.

Identifiers can be PL/I keywords or programmer-defined names. Because PL/I can determine from the context if an identifier is a keyword, you can use any identifier as a programmer-defined name. There are no reserved words in PL/I. However, using some keywords, for example, IF or THEN, as variable names might make a program needlessly hard to understand.