Documentation:OCLOperators append

->append ( object : T ) : Sequence(T)

Returns a Sequence containing all elements of self followed by object.

Expression	Result
Sequence{'a', 'b'}->append('c')	Sequence{'a', 'b', 'c'}

Note! Append does NOT change the "source" sequence. If you want to add an object to an association, use .add

The opposite, excluding an object from a collection without changing the "source" collection - use excluding.