Message: Inheritance is not intended for the data type "UNION" <data type name>.

Possible error cause: A structured data type (‎DUT‎) is derived from a ‎UNION‎ by extending with ‎EXTENDS‎, or a ‎UNION‎ is derived from a ‎DUT‎. This kind of derivation is not permitted. However, for reasons of compatibility only a warning is issued.

Example of the error

TYPE U_StringExt EXTENDS U_StringBase :
UNION
	str10 : STRING(10);
END_UNION
END_TYPE TYPE U_StringBase :
UNION
	str20 : STRING(20);
END_UNION
END_TYPE PROGRAM PLC_PRG
VAR
	uStringExt : U_StringExt;
END_VAR

uStringExt.str20 := 'a234567890b234567890'; -> C0542