The operator is an extension of the IEC 61131-3 standard.
You can use the name of a global variable list (GVL) as a namespace identifier for
the variables that are defined in the list. This makes is possible to use variables
with the same name in different global variable lists and still access specific variables
uniquely. You use a dot (.) to prepend the name of the global variable list to the variable name.
<global variable list name>.<variable>
Example
globlist1.varx := globlist2.varx;
The globlist1 and globlist2 global variable lists each contain a varx variable. CODESYS copies the varx global variable from the globlist2 list to varx in the globlist1 list.
If you reference a variable that is declared in several global variable lists without referencing the prepended list name, then an error message is printed.