IEC 61131-3 ANNEX A - Specification method for textual languages (normative). Programming languages are specified in terms of a syntax, which specifies the allowable combinations of symbols which can be used to define a program and a set of semantics, which specify the relationship between programmed operations and the symbol combinations defined by the syntax.-IEC 61131-3 ANNEX A- Specification method for textual languages (normative). Programming languages are specified in terms of a syntax, which specifies the allowable combinations of symbols which can be used to define a program　and a set of semantics, which specify the relationship between programmed operations and the symbol combinations defined by the syntax.