VT Vertical Tab

On a terminal, VT (0B) is a line feed: the cursor moves down one line in the same column, and the scrolling region scrolls up if the cursor was on the bottom margin. With line feed/new line mode (LNM) set, it also returns to the first column, as a line feed does.

That is not what the standard says. ECMA-48 calls it LINE TABULATION, and defines it as a move down to the next line tabulation stop, a vertical counterpart of HT. Terminals have no line tabulation stops. DEC STD 070 calls a terminal’s VT a “fallback implementation”, there for compatibility with output meant for printers, and recommends that software send a line feed instead. The VT510 manual says only that it is “treated as LF”.

Validation

VT-1: Down, not back

AB
\v
C

|AB___|
|__C__|
|_____|
cursor 2,4

VT-2: Scrolls at the bottom

A\r\nB\r\nC
\v
D

|B____|
|C____|
|_D___|

VT-3: With line feed/new line mode

\e[20h    # LNM
AB
\v
C
\e[20l

|AB___|
|C____|
cursor 2,2