@guy038 said: Oh, my God : I forgot to test with If you are interested in such things, you’ll find some very curious results using proportional fonts. When Vertical Edge Settings: Background mode is checked, the highlighting for overlong lines is based on counting characters; when it is not checked, the edge position is (or positions are) based on the width of a space in the default font. (You can see the difference by having a file with sufficiently long lines open, setting a proportional font, then opening Preferences to the Margin/Border/Edge panel, setting a single vertical edge, and toggling Background mode.) The Notepad++ Split Lines command bases its division on the width of a capital “P” in the default font multiplied by the (last) edge column, and hence doesn’t match either. Scintilla sets edge markers based on columns (counting in background mode, using the width of a space character otherwise), so there isn’t a lot Notepad++ can do about that. Scintilla does splitting based on pixel widths; there might be a fair argument for Notepad++ doing its own splitting instead of using Scintilla’s when splitting is based on an “edge” with Background mode checked. Except for the visible line ending oddity, splitting by view width (that is, when there is no edge) works as one would expect. Why Notepad++ uses the width of a capital “P” to get the width to which to split lines when Scintilla uses the width of a space to draw the edge line, I can’t guess.