DECSLRM Set Left and Right Margins

Set the left margin to column Pl and the right margin to column Pr. Together with the top and bottom margins that DECSTBM sets, they bound the scrolling region. Text written inside them wraps at the right margin back to the left one, and scrolling, insertion and deletion move only what is inside. A parameter left out, or 0, takes its default.

As with DECSTBM, the left margin has to be left of the right one, and DEC STD 070 ignores the control otherwise. Setting the margins moves the cursor to the home position, obeying origin mode.

DECSLRM works only while left right margin mode, DECLRMM, is set with CSI ? 69 h. DEC STD 070 defines the mode at §5.4.3, p. 5-29, and the VT510 manual as DECLRMM—Left Right Margin Mode. Resetting it with CSI ? 69 l puts the left and right margins back at the edges of the screen. It is off by default.

The mode exists because CSI s already meant something. In SCO console mode, CSI s with no parameters saves the cursor position and CSI u restores it (SCOSC and SCORC in the VT510 manual). So xterm reads CSI s as DECSLRM while DECLRMM is set, and otherwise as a save of the cursor if it has no parameters (CASE_ANSI_SC). DEC STD 070 makes DECSLRM, like DECLRMM, part of level 4 with the horizontal scrolling extension; xterm accepts DECLRMM only when emulating a VT420 or later (srm_DECLRMM), while libghostty-vt always does.

Validation

DECSLRM-1: Ignored without DECLRMM

\e[1;3H
\e[2;4s   # DECLRMM is off, so not DECSLRM
X

|__X___|
|______|
cursor 1,4

DECSLRM-2: Text wraps at the right margin

\e[?69h   # DECLRMM
\e[2;4s   # columns 2 to 4; the cursor goes home
abcdefgh
\e[?69l   # off again: the margins are the screen's
\e[1;1H
ABCDEFGH

|ABCDEFGH|
|_efg____|
|_h______|

DECSLRM-3: A left margin not left of the right is ignored

\e[2;5H
\e[?69h
\e[3;3s

|________|
|________|
cursor 2,5

DECSLRM-4: Homes to the margin in origin mode

\e[?69h
\e[?6h    # origin mode
\e[3;5s

|________|
|________|
cursor 1,3

DECSLRM-5: Without DECLRMM, CSI s saves the cursor

\e[2;3H
\e[s      # SCOSC
\e[1;1H
\e[u      # SCORC
X

|________|
|__X_____|

DECSLRM-6: With DECLRMM, CSI s resets the margins

\e[?69h
\e[2;4s
\e[2;3H
\e[s      # DECSLRM with both left out
abcdefgh

|abcdefgh|
|________|

DECSLRM-7: Asking about DECLRMM

\e[?69$p  # reset
\e[?69h
\e[?69$p  # set

|________|
reply \e[?69;2$y\e[?69;1$y