https://www.scintilla.org/ScintillaDoc.html#SCI_COPY
copying data to the clipboard
Is document to the clipboard.
https://www.scintilla.org/ScintillaDoc.html#SCI_PASTE
pasting from the clipboard into the document
Is clipboard to the document.
Both functions relate to the document in the editor. The copy function will be good for the task though paste will not work with the search window.
Instead of SCI_PASTE, could use the Run command to run an executable to insert the clipboard text into the search window.
AutoIt3 script automate_columns++_search.au3 :
; Wait up to 3 seconds for the window. $hSearch = WinWait('Search in indicated region', '', 3) If $hSearch Then $sClip = ClipGet() ; get clipboard text ControlSetText($hSearch, '', 'Edit1', $sClip) ; set combo edit ControlClick($hSearch, '', 'Button7') ; click regex button ControlClick($hSearch, '', 'Button9') ; click count button $sCount = ControlGetText($hSearch, '', 'Static3') ; read label ClipPut($sCount) ; set clipboard text EndIfAdjust the title if the window text is localized.
Compile to executable and then add to Run as a command. Get the command id with NppUISpy and insert into the shortcuts.xml file.