Begin if condition.
.IF expression [ THEN]
stmtlist
[ .ELSE
stmtlist]
.ENDI
If expression is true, execute stmtlist following THEN (the keyword THEN is optional); if expression is false, execute stmtlist following .ELSE, if present; otherwise, advance to the instruction following .ENDI.
In the case of nested .IF- THEN- .ELSE statements, each .ELSE refers to the most recent .IF- THEN sequence.
.IF <EQ> ; zero bit set?
...ENDI