> Rather, a tab, at least when rendered onto a PTY, advances the cursor to the next tabstop — i.e. to the next virtual column that is a multiple of 8. Multiple

> Rather, a tab, at least when rendered onto a PTY, advances the cursor to the next tabstop — i.e. to the next virtual column that is a multiple of 8. Multiple of 8 is just convention, though. AFAIU, it's up to the display software--editor, terminal emulator, etc--where to place tab stops. The kernel TTY and PTY layers don't know anything about tab stops, AFAIU. In the case of terminals there are control sequences available for programs to query and update the tab stops; but all the logic is still at the ends. Contrast that with line buffering and certain escape sequences, where character sequences are captured and interpreted by the terminal device driver. Also note that it's tab stops, plural. The default tab stops are multiples of 8, but you can tell a terminal (similar to other display software, like MS Word) to place tab stops at discrete positions that aren't multiples of anything, e.g. 10, 12, 18, 27, etc.