Document promise_to_disable_if_enabled.

diff --git a/theme.rst b/theme.rst
index 2e8b6663b0ccddd05fe1314502ff9c5d2cf040f5..dbfdebe8e684ba302f8fe74498b212bf7775ece1 100644 (file)
--- a/theme.rst
+++ b/theme.rst
@@ -399,6 +399,17 @@ crop is. If so, you can do this::
 
    resample_effect:always_disable_if_disabled(crop_effect)
 
 
    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
 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