SM Set Mode

CSI Pm h sets one or more modes. Each parameter names one mode, the modes are set in order, and ECMA-48 gives no default. RM, CSI Pm l, resets them again.

ECMA-48 numbers 22 modes, most of them for block-mode terminals, editing devices and bidirectional text, and each has a page under ANSI modes. DEC STD 070 lists only four a DEC terminal accepts, KAM, IRM, SRM and LNM, and says that a 0 is an error and is ignored; the VT220 manual’s table of ANSI modes is the same. xterm and libghostty-vt accept the same four (ansi_modes) and ignore every other number. They differ only in what DECRQM says about the rest:

Only IRM and LNM change what appears on the screen, so they are the ones the cases here use.

ANSI modes and DEC private modes cannot be mixed in one sequence. The DEC private form, CSI ? Pm h, is DECSET, and its numbers name the private modes.

Support

Validation

SM-1: Two modes in one sequence

abc
\e[1;1H
\e[4;20h  # IRM and LNM
X
\n
Y

|Xabc_|
|Y____|
cursor 2,2

SM-2: A mode that is not known does not stop the others

abc
\e[1;1H
\e[0;99;4h # 0 is an error, 99 is no mode
X

|Xabc_|
cursor 1,2

SM-3: A question mark makes it a different mode

abc
\e[1;1H
\e[?4h    # DECSCLM, smooth scrolling, not IRM
X

|Xbc__|
cursor 1,2