All,

   The help documentation for kde3/trinity does not include information on the 
katepart find/replace dialog "Placeholders" text entry box, checkbox or button. 
Searching, I found where it was later added in KDE4.

https://docs.kde.org/trunk4/en/kde-runtime/fundamentals/find.html

   A somewhat expanded version of that help is included below. I opened a eature 
request http://bugs.pearsoncomputing.net/show_bug.cgi?id=2558 (dunno if Darrell 
is still the help Maestro, so it is there for anyone to patch/submit - I don't 
have a current clone of the repo or I'd do it.):

Replacement Text

     Here you may enter the text to replace the text or expression entered in 
the "Text to find:" entry combobox.

     You can reuse all or part of the "Text to find:" text or expression in the 
"Replacement text" by selecting the "Use placeholders" checkbox. Placeholders, 
also known as 'backreferences', are a special character sequence that will be 
replaced with all or part of the original text or expression. They offer a 
short-cut to entering a full "Replacement text" expression. For instance, by 
default "\0" represents the complete 'pattern space' matched as a result of the 
text or expression entered in the "Text to find:" box. (a backreference to the 
entire matched string).

     You may insert placeholders into the "Replacement text" box by clicking the 
"Insert Placeholder" button, then selecting an option from the menu like 
'Complete Match'. For example, if you are searching for "message", and you want 
to replace it with messages insert the Complete Match placeholder and add and 
"s". The replace field will then contain "\0s".

     If Kate is installed, you can learn more about placeholders in the 'Regular 
Expressions' appendix of its documentation.


-- 
David C. Rankin, J.D.,P.E.