->append ( object : T ) : Sequence(T)

The append() operator is used to add an element to the end of a collection, returning a new collection that includes the added element. It does not modify the original collection but produces a new one with the additional item. This operator is typically used with ordered collections such as Sequence or OrderedSet, where the position of elements matters

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.