WebClient has upper limits on the total number of VisualComponents and temporary files cached. That means some older cached items are deleted if WebCache is full.
WebCache is not implemented in the Memento pattern[ralph's book] because each cache item related to each HyperLink has a temporary file and sometimes also a VisualComponent. WebCache has an upper limit on the total number of Filenames and VisualComponents stored. The filenames removed from WebCache is deleted from the temporary directory. WebCache needs to know the internal structures of the cached items and this violates the essence of Memento.