Some collections cannot be mutated once they have been created. As listed about, a few other operations are supported: Membership testing ( Contains), resetting ( Clear), copying of the collection to an array ( CopyTo), and measuring of size ( Count).
At this level of abstraction, it is not specified where in the collection an element is added. In addition to traversability, elements of type T can be added to and removed from objects of type ICollection.
The PDF version is an almost complete subset of the HTML version (where only a few, long program listings have been removed). A complete PDF version of the text book is now available.