The Task in the KDE Phabricator was: https://phabricator.kde.org/T2040

A first version was implemented with: rKLEOPATRA20ba50d44c28dd4e4f60eb67de00db07e0d60211

And can be seen in action: https://files.intevation.de/users/aheinecke/notepad-mode.gif