# Focus Events (?1004)

> Have the terminal tell the program when its window gains or loses the keyboard focus.

- **Sequence:** `CSI ? 1004 h/l`
- **xterm:** [Mouse Tracking](https://invisible-island.net/xterm/ctlseqs/ctlseqs.html)

With `CSI ? 1004 h` set, the terminal sends `CSI I` to the program when its
window gains the keyboard focus and `CSI O` when it loses it, so that an
editor can, for instance, reload a file that changed while it was in the
background. `CSI ? 1004 l` stops the reports. It is xterm's, listed with the
[mouse tracking](https://control-codes.page/modes/mouse/index.html.md) modes, but it can be set with or without any
of them
([`dpmodes`](https://github.com/ThomasDickey/xterm-snapshots/blob/xterm-411a/charproc.c#L7827-L7831),
[`SendFocusButton`](https://github.com/ThomasDickey/xterm-snapshots/blob/xterm-411a/button.c#L5676-L5712)).
It is off to begin with, and [RIS](https://control-codes.page/esc/ris/index.html.md) turns it off.

Focus changes come from the window, not from the data a case writes, so the
cases check what DECRQM says and that setting the mode sends nothing on its
own. libghostty-vt passes them.

## Support

| Terminal | Version | Support | Notes |
| --- | --- | --- | --- |
| VT220 | [manual](https://vt100.net/docs/vt220-rm/), 2nd ed., 1984 | No | not in the manual |
| VT510 | [manual](https://vt100.net/docs/vt510-rm/), 1st ed., 1993 | No | not in the manual; not in [Table 5-6](https://vt100.net/docs/vt510-rm/DECRPM.html) |
| xterm | patch 412, [xterm-411a](https://github.com/ThomasDickey/xterm-snapshots/tree/xterm-411a) | Yes |  |
| libghostty-vt | [0f171f6](https://github.com/ghostty-org/ghostty/tree/0f171f650a1cbbd6df4a2573b6b0c7de57cc6d90) | Yes |  |
| kitty | 0.49.1, [run in a VM](https://git.jcollie.dev/jeff/control-codes/src/branch/main/emulators/results/kitty.json) | Yes | passes the 3 cases that show it working |
| foot | 1.28.0, [run in a VM](https://git.jcollie.dev/jeff/control-codes/src/branch/main/emulators/results/foot.json) | Partly | fails FOCUS-3, FOCUS-4 of the 3 cases that show it working |
| xterm.js headless | 6.0.0, [run as a library](https://git.jcollie.dev/jeff/control-codes/src/branch/main/emulators/results/xtermjs.json) | Yes | passes the 3 cases that show it working |
| alacritty_terminal | 0.26.0, [run as a library](https://git.jcollie.dev/jeff/control-codes/src/branch/main/emulators/results/alacritty.json) | Yes | passes the 3 cases that show it working |
| ConEmu | build 230724, its [documentation](https://conemu.github.io/en/AnsiEscapeCodes.html) | Yes | listed among the mouse modes, as `FOCUS_EVENT_MOUSE`; [ANSI escape codes](https://conemu.github.io/en/AnsiEscapeCodes.html) |
| rxvt-unicode | 9.31, [run in a VM](https://git.jcollie.dev/jeff/control-codes/src/branch/main/emulators/results/urxvt.json) | Partly | fails FOCUS-4 of the 3 cases that show it working |
| VTE | 0.84.1, [run as a library](https://git.jcollie.dev/jeff/control-codes/src/branch/main/emulators/results/vte.json) | Partly | fails FOCUS-3, FOCUS-4 of the 3 cases that show it working |

## Validation

### FOCUS-1: Off to begin with

Input, one step per line:

```text
\e[?1004$p
```

Expected screen:

```text
|____|
reply \e[?1004;2$y
```

### FOCUS-2: Setting it sends nothing

Input, one step per line:

```text
A
\e[?1004h
B
```

Expected screen:

```text
|AB__|
cursor 1,3
reply none
```

### FOCUS-3: Set and reset

Input, one step per line:

```text
\e[?1004h
\e[?1004$p
\e[?1004l
\e[?1004$p
```

Expected screen:

```text
|____|
reply \e[?1004;1$y\e[?1004;2$y
```

### FOCUS-4: RIS turns it off

Input, one step per line:

```text
\e[?1004h
\ec
\e[?1004$p
```

Expected screen:

```text
|____|
reply \e[?1004;2$y
```

---

This is the Markdown version of <https://control-codes.page/modes/focus/>. 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>.