FF Form Feed

Move the cursor down one line, exactly as a line feed does.

FF

ECMA-48: §8.3.51 FF – Form Feed, p. 44
DEC STD 070: §5.4.4 Form Feed, p. 5-62
VT220: §4.2 Control Characters
VT510: 4.2 Control Characters

On a terminal, FF (0C) 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 defines it as a move to the page home position of the next page or form, which is what a printer does with it. A terminal does not clear its screen or start a new page. DEC STD 070 calls a terminal’s FF 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”.

Support

Terminal	Version	Support	Notes
VT220	manual, 2nd ed., 1984	Yes	§4.2 Control Characters
VT510	manual, 1st ed., 1993	Yes	Table 4–1
xterm	patch 412, xterm-411a	Yes	processed as LF
libghostty-vt	0f171f6	Yes	processed as LF
kitty	0.49.1, run in a VM	Yes	passes the 3 cases that show it working
foot	1.28.0, run in a VM	Partly	fails FF-3 of the 3 cases that show it working
pyte	0.8.2, run as a library	Yes	passes the 3 cases that show it working
xterm.js headless	6.0.0, run as a library	Yes	passes the 3 cases that show it working
alacritty_terminal	0.26.0, run as a library	Partly	fails FF-3 of the 3 cases that show it working
rxvt-unicode	9.31, run in a VM	Partly	fails FF-3 of the 3 cases that show it working
VTE	0.84.1, run as a library	Partly	fails FF-3 of the 3 cases that show it working

Validation

FF-1: Down, not back

AB
\f
C

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

FF-2: Scrolls at the bottom

A\r\nB\r\nC
\f
D

|B____|
|C____|
|_D___|

FF-3: With line feed/new line mode

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

|AB___|
|C____|
cursor 2,2