A Patch describes the changes made to a List.
A Patch saying, that one or more elements have been deleted
A Patch saying, that a new element has been inserted
A Patch saying, that a several element have been inserted
A Patch saying, that an element has been moved from one position to another. This is only used on mounts with a corresponding IdProvider.
a convenience-method, to map the values encapsulated in a Patch