The FILTER command is used to append to or replace the current path name filter. If the current display is a personal list, then the filter can only be replaced.

                   .-APPEND--.   
>>-FILTER--string--+---------+---------------------------------><
                   '-REPLACE-'   

If the current filter is /u/harry/test* then
FILTER p
changes the filter to /u/harry/test*p.

The REFRESH command restores the entry value.