All of the choices for a viewer can be stored locally for that viewer. The stored information can optionally apply to all subdirectories as well. Seperate options for each file-operation, e.g. turn on Confirm for delete, but not for everything else. Cache system for thumbnails, and option to save pieces of the cache in the places where it will be needed. Service calls, wimp messages and SWIs allow applications to take advantage of the Filer's extended abilities.
System variables allow easy extensions without having to program.
External Utilities are supported, functions can be added to the filer menus. One simple Basic program is enough to make a converter utility.