How to implement reverse deletion in Notepad++?

Question

Notepad++

I highlighted the words in Notepad++. Now you need to delete all the lines in which words are not highlighted, and ideally, you need to delete the lines where there is no selection, and leave the line where there are highlights, plus leave three lines under the line with the selected text. Is it possible to do such a manipulation in this program, and if so, how?

Answer 1

If you want to replace xxx with yyy, then
1) In the selection, replace xxx with zzz
2) Throughout the document, replace xxx with yyy
3) Throughout the document, replace zzz with xxx
That's it.