There seems to be a difference in an IF() function if the condition
includes a variable, and if the variable is prefixed by a full colon (:)

Example: IF(V_MYVAR IS NULL) THEN
versus IF(:V_MYVAR IS NULL) THEN

FB 2.01 will not complain about either syntax.
Which is correct? Include the semi-colon or not?
And, in other cases, like subsequent UPDATEs or SELECTs (after the
select that loaded the variable in the first place) should I include
the full colon or not?

Thanks in advance for any help.