I'm not sure exactly what the "other" expression would refer to. In your description it seems to be defined as "a magic expression that does what I want". What exactly would it refer to? There are a great many "other instances" it could potentially refer to, how should the engine pick which one you mean? Also in your example "Self" and "Other" are used as object type names, which are not object instances.
sorry it would return the other instance of a condition not a event
like for say if placed inside a (is overlapping event) or a (on collision of another object) condition it would return the object it would return the object chosen in that event
however if it was placed in a event like (is between angles)
it would normal return (null ,nil, -1)
however if it was placed in a (is between angles) in a (is overlapping event) or a (on collision of another object) condition it would return the object it would return the object chosen in the collision event
basicly it would return the other instance in a condition if there was one
else would return a null value or -1