I am using SciTE . This is an example of a Scintilla project, a free source code editing component.
Edit: Notepad ++ also uses Scintilla in the kernel. I tested it (beautiful plugins) and found that it was a bit buggy and slow, one of the examples that came to mind was editing the source file 350,000, then vertically highlighting several columns from top to bottom and copying this text, open a new file and then insert - you have to wait for the selection!
I returned to SciTE - fast and stable (like Scintilla).
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