Terminal Identification

The BBS asks each caller's terminal what it is, in the way DEC's terminals were asked, and adapts to the answer. Real VTs (and emulators set up as one) get their own line drawing and character set, monochrome terminals get bold instead of colour, and a VT52 gets its own escape codes. The terminal's answer appears in Who's online through the HTTP API (terminal), in the caller's profile, and in the log:

node 3: terminal VT220 (DA1 62;1;2;6;7;8;9, DA2 1;10;0)
node 4: terminal XTerm(390) (DA1 64;1;2;4;6;9;15;16;17;18;21;22;28, DA2 41;390;0, version XTerm(390))
node 5: terminal tmux 3.4 (DA1 1;2;4, DA2 84;0;0, version tmux 3.4)

The questions

An ANSI terminal is sent all of these questions at once:

Sent	Asks for	Answered by
ENQ	the answerback message	terminals with one set (PuTTY says PuTTY)
CSI c	primary device attributes (DA1): the VT level and options	every VT100 and later, xterm, most emulators; SyncTERM in its CTerm form
CSI > c	secondary device attributes (DA2): the model and firmware	VT220 and later, xterm, VTE, tmux, screen, mintty
CSI > 0 q	XTVERSION: name and version	xterm, tmux, foot, kitty, WezTerm, iTerm2
CSI 16 t	the character cell in pixels (for sixel)	xterm and others
CSI 6 n	the cursor position	every ANSI terminal; by the time it arrives, the other answers have too

The position report comes last, so the BBS waits only for it rather than for a timeout, even on a terminal that answers none of the others. If a terminal is not ANSI (it did not answer the BBS's first question, the cursor position), the BBS sends it a VT52's identify request, ESC Z. A VT52 answers with ESC / Z; any other terminal shows a Z, which the BBS then wipes.

What it is called

The BBS names the terminal from the first of these that applies:

1. the name in its XTVERSION answer;
2. SyncTERM, from its CTerm attributes;
3. a VT52;
4. a DEC terminal, from its DA2 model (VT100, VT220, VT240, VT320, VT330, VT340, VT382, VT420, VT510, VT520, VT525, DECterm) with a DEC firmware version;
5. an emulator, from its DA2 (tmux, screen, mintty, rxvt, xterm by its patch number, VTE);
6. its answerback;
7. the VT class from DA1 (VT100, VT102, VT200 class ... VT500 class).

What it changes

• DEC character sets. A VT (DA1 says VT100 or later) whose terminal type does not say UTF-8 and which is not a PC's BBS terminal (ansi, syncterm and the like, which want CP437) gets line drawing and blocks in DEC Special Graphics (ESC ( 0, the lqkxjm characters), Latin-1 letters as 8-bit characters on a VT220 or later (DEC Multinational has them) on an 8-bit line, and ASCII look-alikes for the rest. ANSI art in CP437 is drawn the same way. Typed Latin-1 letters are read as such. The profile says DEC graphics.
• Monochrome. A DEC terminal by its model and firmware (not an emulator) without ANSI colour (DA1 option 22), from the VT100 to the VT520, gets bold for the bright colours and plain text for the rest.
• Sixel is known from DA1 option 4 (a VT240, VT330, VT340, xterm with it on, foot, WezTerm, mlterm), and the cell size from CSI 16 t.
• VT52. A VT52 (or a VT100 in VT52 mode) gets clearing and cursor movement as ESC H, ESC J, ESC K, ESC Y, ESC A-D, no attributes, ASCII only; its cursor and keypad keys are not taken as commands.

Turning it off

[listen modem]
type = raw
address = 127.0.0.1:2323
vt = no

With vt = no the BBS asks none of these questions and changes nothing (it still checks for sixel with DA1 alone). auto, the default, asks.

What a caller sets

Settings a caller changes in their profile are kept with their account and apply from their next call:

Setting	Values	At the next call
ansi	on, off	ANSI as they set it, whatever the terminal answered (off turns RIP off too)
utf8	on, off	UTF-8, or CP437 (ASCII where there is no ANSI)
sixel	on, off	off keeps sixel off; on only where the terminal says it has it
rip	on, off	the same for RIPscrip
width	40, 80	a Commodore's columns
editor	full, line	the full-screen editor or the line editor
expert	on, off	menus as their prompt alone, ? for the rest

A Commodore or a VT52 uses only the settings that apply to it. The settings appear as prefs at GET /api/v1/me and are changed with PATCH /api/v1/me (see HTTP API).

See also: PETSCII and RIP, Sixel graphics, Configuration