The function returns a column count of the structured variable (or structure definition) as a number. HBJ expression returns an attribute \HBJ of an object.
Example
%GetColsNr(SD.Struktura\HBJ) ; it returns a column count
%GetColsNr(SV.Struktura\HBJ) ; it returns a column count
%GetColsNr(Sec\HBJ) ; it returns an invalid value