resample_effect:always_disable_if_disabled(crop_effect)
+Also, since Nageru 1.9.1, you can disable an optional effect if a given other
+effect is *enabled*::
+
+ overlay1_effect:promise_to_disable_if_enabled(overlay2_effect)
+ overlay2_effect:promise_to_disable_if_enabled(overlay1_effect)
+
+Note that the latter is a promise from the user, not automatic disabling; since
+it is mostly useful for mutual exclusions, Nageru wouldn't know which of the
+two to disable. (If you violate the promise, you will get an error message at
+runtime.) It can still be useful for reducing the number of alternatives, though.
+
For more advanced exclusions, you may choose to split up the scenes into several
distinct ones that you manage yourself; indeed, before Nageru 1.9.0, that was
the only option. At some point, however, you may choose to simply accept the