SayHelp screen 4: The Replace filter (#70315)  [A working example filter]
The Replace filter replaces a list of <search> strings with <replace> strings
wherever it can find them. (You can have different lists on different <ch>s,
but if you set nothing for a given <ch>, the default list will be used [if it
exists]). You may escape spaces '\ ' and escapes '\\'.
To add to a replace list:          sayfilter <ch> add[.n]  <search> <replace>
To remove an item from the list:   sayfilter <ch> take[.n] <item-listnumber>
To list a replace list:            sayfilter <ch> list[.n]
[ You only need use the .n if an earlier filter, 'RandomSplit' in the example,
                                              understands 'add' 'take' 'list' ]
    sayset clear %     [This clears out the % macro]
    sayfilter % fadd replace
    sayset % purrs                sayfilter % list
    sayfilter % add er urr          _say/%/1/1: "er" -> "urr"
    sayfilter % add or orr          _say/%/1/2: "or" -> "orr"
    sayfilter % add \ is\  's\      _say/%/1/3: " is " -> "'s "
    (Continue with next column)   "%It is perfectly normal,,
                                  "%It's purrfectly norrmal," purrs KittyKat.
sayhelp 5 (rooms/envs)  6 (puppets)  7,8,9 (filter-writing)  10 (boringadmin)