# Character Editing Mode (HEM)
> Which way characters move when one is inserted or deleted.
- **Sequence:** `CSI 10 h`
- **ECMA-48:** [§7.2.9 HEM – Character Editing Mode, p. 23](https://archive.org/details/ecma-48-5th-edition-june-1991/page/n36/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 10 decides which characters move when one is inserted with
[ICH](https://control-codes.page/csi/ich/index.html.md) or deleted with [DCH](https://control-codes.page/csi/dch/index.html.md). DEC STD 070 calls it Horizontal Editing Mode.
| State | ECMA-48 calls it | Meaning |
| --- | --- | --- |
| Reset, `CSI 10 l` | FOLLOWING | the characters at and after the cursor move right for an insertion, and left to close a deletion |
| Set, `CSI 10 h` | PRECEDING | the characters before the cursor move left for an insertion, and right to close a deletion |
[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. That is the way ICH and DCH work in xterm and libghostty-vt.
xterm ignores `CSI 10 h` and `CSI 10 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
### HEM-1: Reported as permanently reset
*A known difference: libghostty-vt does not pass this case.*
Input, one step per line:
```text
\e[10$p
```
Expected screen:
```text
|_____|
reply \e[10;4$y
```
### HEM-2: Even after it is set
*A known difference: libghostty-vt does not pass this case.*
Input, one step per line:
```text
\e[10h
\e[10$p
```
Expected screen:
```text
|_____|
reply \e[10;4$y
```
### HEM-3: ICH still pushes the characters after the cursor right
Input, one step per line:
```text
abc
\e[10h # ignored
\e[1;2H
\e[@
```
Expected screen:
```text
|a_bc_|
cursor 1,2
```
---
This is the Markdown version of . 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 .