conditional expansion. It takes the following forms:
@example
-!IF (condition) !THEN true-expansion !ENDIF
-!IF (condition) !THEN true-expansion !ELSE false-expansion !ENDIF
+!IF (condition) !THEN true-expansion !IFEND
+!IF (condition) !THEN true-expansion !ELSE false-expansion !IFEND
@end example
When the @var{condition} evaluates to true, @var{true-expansion} is