# Set X Property (OSC 3)

> Set or delete a property on the terminal's top-level X window.

- **Sequence:** `OSC 3 ; prop = value ST`
- **ECMA-48:** [§8.3.89 OSC – Operating System Command, p. 51](https://archive.org/details/ecma-48-5th-edition-june-1991/page/n64/mode/1up)
- **xterm:** [Operating System Commands](https://invisible-island.net/xterm/ctlseqs/ctlseqs.html)

`OSC 3 ; prop=value ST` sets the property `prop` of xterm's top-level X
window to `value`, and `OSC 3 ; prop ST` deletes it, so that a program can
leave information on the window for the window manager or for scripts that
look at X properties
([`ChangeXprop`](https://github.com/ThomasDickey/xterm-snapshots/blob/xterm-411a/misc.c#L6380-L6401)).
The number came from dtterm, which used it to set the working directory for
the next session; xterm does that with its `spawn-new-terminal` action
instead.

A default xterm does not do it. Setting a property is one of the *window
operations* off unless `allowWindowOps` is set: `SetXprop` is in the
default `disallowedWindowOps`
([`main.h`](https://github.com/ThomasDickey/xterm-snapshots/blob/xterm-411a/main.h#L150-L175),
[`do_osc`](https://github.com/ThomasDickey/xterm-snapshots/blob/xterm-411a/misc.c#L4183-L4187)).
X properties do not exist outside X, and libghostty-vt has no `OSC 3`: it
ignores it. Both leave the screen and the title as they were, and the cases
pass.

## Validation

### OSC3-1: Nothing changes

Input, one step per line:

```text
\e]2;Window\a
A
\e]3;WM_ROLE=terminal\a
\e]3;WM_ROLE\a   # delete it
B
```

Expected screen:

```text
|AB____|
cursor 1,3
title "Window"
reply none
```

---

This is the Markdown version of <https://control-codes.page/osc/x-property/>. On that page every validation case runs live in libghostty-vt, the terminal emulation core of Ghostty, compiled to WebAssembly.

The validation cases are written in the notation described in <https://control-codes.page/notation/index.html.md>.