I have a little fantasy console project I tinker on that has a built-in text editor. Working on that has been an insightful trip into all of the subtleties of t

I have a little fantasy console project I tinker on that has a built-in text editor. Working on that has been an insightful trip into all of the subtleties of text editing that we intuitively know but don't know we know. Here's one I stumbled onto recently. Say your file looks like this, with the cursor at `|`: 12345|678 123 12345678 Press arrow key down once, and you get: 12345678 123| 12345678 Because the second line's length is too short to preserve the cursor column, the cursor snaps to the end of the line. Note that the cursor is really here. If the user were to press left once, it would take them to: 12|3 Instead of pressing left, say the user presses down again. The cursor is currently on column 4, so you'd expect: 12345678 123 123|45678 But in the text editors I've tested, you get: 12345678 123 12345|678 So the cursor is snapped to the end of the line on line 2, but if the user keeps cursoring past that, the original cursor column is remembered and restored. The text editor has to display where the cursor currently is, but track where it "wants" to be if the line length weren't getting in the way. This is definitely useful behavior. If you arrow down through a bunch of lines of various lengths, it's really annoying if the cursor starts drifting left. But implementing it correctly was much more subtle than I expected. There are all sorts of other edge cases too. If a user presses Command-Up to move the cursor to the beginning of the file, and then presses Down, does the cursor always stay on column one, or does it remember the original column before Command-Up was pressed?