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PLCOPEN-N8: Define the acceptable character set

Identifiers must only contain ASCII letters, digits and underscores, and must not start with a digit.

Why is it bad?​

IEC 61131-3 is an international standard but the identifier grammar is intentionally narrow. Accented characters, non-Latin scripts and digits-as-first-characters travel badly across editors, vendor IDEs, source control and code review tools — they turn into mojibake, break grep and get silently rewritten during import/export. Sticking to [A-Za-z_][A-Za-z0-9_]* keeps every downstream tool honest.

Example​

PROGRAM program0
  VAR
    départ : BOOL;    (* PLCOPEN-N8 — accented character *)
    3axis  : INT;     (* PLCOPEN-N8 — starts with a digit *)
    Depart : BOOL;    (* ok *)
  END_VAR
END_PROGRAM

The examples above would be rejected by the Structured Text lexer before PLCOPEN-N8 gets a chance to look at them. The main use-case for this lint is programs imported from PLCOpen XML or SEL XML, where identifiers go through a different pipeline and non-ASCII names can slip in.

Resources​

  1. PLCOpen Software Construction Guidelines