# Positioning Unit Mode (PUM)

> Whether cursor movement counts in characters or in SSU units.

- **Sequence:** `CSI 11 h`
- **ECMA-48:** [§F.4.1 PUM – Positioning Unit Mode, p. 87](https://archive.org/details/ecma-48-5th-edition-june-1991/page/n100/mode/1up)
- **DEC STD 070:** [§5.10.1.3 Modes That Cannot Be Changed, p. 5-134](https://archive.org/details/bitsavers_decstandar0VideoSystemsReferenceManualDec91_74264381/page/n388/mode/1up)

Mode 11 decides the unit of the numbers given to the cursor movements,
[CUF](https://control-codes.page/csi/cuf/index.html.md), [HPA](https://control-codes.page/csi/hpa/index.html.md), [HVP](https://control-codes.page/csi/hvp/index.html.md) and the others.
ECMA-48 deprecates it, and moved it to an annex: SSU, Select Size Unit, sets
the unit anyway, and its default is the character.

| State | ECMA-48 calls it | Meaning |
| --- | --- | --- |
| Reset, `CSI 11 l` | CHARACTER | one is one character position |
| Set, `CSI 11 h` | SIZE | one is the unit SSU selects |

[DEC STD 070 §5.10.1.3, p. 5-134](https://archive.org/details/bitsavers_decstandar0VideoSystemsReferenceManualDec91_74264381/page/n388/mode/1up) lists it among the X3.64 modes a DEC terminal may treat as fixed,
as reset. The VT510 manual's [table of modes for DECRPM](https://vt100.net/docs/vt510-rm/DECRPM.html) marks it as always reset.

xterm ignores `CSI 11 h` and `CSI 11 l` ([`ansi_modes`](https://github.com/ThomasDickey/xterm-snapshots/blob/xterm-411a/charproc.c#L7399-L7424) handles only modes 2,
4, 12 and 20), and [DECRQM](https://control-codes.page/csi/decrqm/index.html.md) reports the mode as permanently
reset, `4` ([`do_ansi_rqm`](https://github.com/ThomasDickey/xterm-snapshots/blob/xterm-411a/misc.c#L5408-L5463)). libghostty-vt ignores it too, but does not recognize the
number, so it answers DECRQM with `0`. Both DECRQM cases are known
differences.

## Validation

### PUM-1: Reported as permanently reset

*A known difference: libghostty-vt does not pass this case.*

Input, one step per line:

```text
\e[11$p
```

Expected screen:

```text
|_____|
reply \e[11;4$y
```

### PUM-2: Even after it is set

*A known difference: libghostty-vt does not pass this case.*

Input, one step per line:

```text
\e[11h
\e[11$p
```

Expected screen:

```text
|_____|
reply \e[11;4$y
```

### PUM-3: Movement still counts characters

Input, one step per line:

```text
\e[11h     # ignored
\e[3C
A
```

Expected screen:

```text
|___A_|
cursor 1,5
```

---

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