An Iterator object navigates through all objects of a List which can be one of the classes derived from the ListMgr base class.
Filters enumerate on top of iterators and filter out a set of objects that match a certain criteria.
Iterator and Filter objects are generated and destroyed dynamically at run time by application programs, in order to navigate compound structures. Iterative classes reduce the dependancy between application programs, and the underlying compound structure such that modifying the compound structure has minimal impact on application programs. All entities of a compound. All polymer entities. All secondary structures in the list.