A clause consisting only of blanks or comments or both is a null clause. It is completely ignored (except that
if it includes a comment it is traced, if appropriate).
Note: A null clause is not an instruction; for example,
putting an extra semicolon after the THEN or ELSE in an IF instruction
is not equivalent to using a dummy instruction (as it would be in
PL/I). The NOP instruction is provided for this purpose.