{
  "id": "terminal-dec-private-mode/12",
  "family": "terminal-dec-private-mode",
  "slug": "12",
  "title": "DECSET 12 — Cursor blink (att610)",
  "summary": "CSI ? 12 h enables text-cursor blinking; CSI ? 12 l makes the cursor steady (no blink). This is the 'att610' cursor-blink private mode popularized by xterm. It controls blink only; the cursor SHAPE is set by DECSCUSR (CSI Ps SP q), and the two can conflict.",
  "kind": "control-sequence",
  "aliases": [
    "att610",
    "cursor blink",
    "DECSET 12",
    "?12h / ?12l",
    "blinking cursor"
  ],
  "status": "de-facto",
  "verification": "verified",
  "tier": "B",
  "source_url": "https://invisible-island.net/xterm/ctlseqs/ctlseqs.html",
  "source_version": "xterm ctlseqs, patch #410, 2026/04/19",
  "retrieved_date": "2026-05-29",
  "attribution": [
    {
      "claim_ref": "#summary",
      "source_url": "https://invisible-island.net/xterm/ctlseqs/ctlseqs.html",
      "source_version": "xterm patch #410, 2026/04/19",
      "note": "xterm ctlseqs: Ps = 1 2 -> Start Blinking Cursor (AT&T 610). Set = blinking cursor, reset = steady cursor."
    }
  ],
  "see_also": [
    "terminal-csi/decscusr"
  ],
  "ext_type": "terminal-escape@1",
  "ext": {
    "csi_or_osc": "DEC-private-mode",
    "command_number": 12,
    "frame": {
      "introducer_7bit": "\u001b[?",
      "introducer_7bit_readable": "ESC [ ? (0x1B 0x5B 0x3F)",
      "introducer_8bit": "›?",
      "introducer_8bit_readable": "0x9B ? (8-bit CSI + '?')",
      "note": "DEC private mode (CSI with '?' private prefix). Set = final byte 'h' (DECSET); reset = final byte 'l' (DECRST). Self-terminating."
    },
    "terminator": "none",
    "terminator_detail": {
      "note": "No string terminator: the enable/disable ends at the final byte 'h'/'l'."
    },
    "params": [
      {
        "id": "set",
        "anchor": "#set",
        "name": "Enable (DECSET)",
        "meaning": "CSI ? 12 h turns ON cursor blinking (att610).",
        "required": true,
        "byte_sequence_ST": "\u001b[?12h",
        "byte_sequence_ST_readable": "ESC [ ? 1 2 h   ==  \\x1b[?12h   (set / DECSET)",
        "subparams": []
      },
      {
        "id": "reset",
        "anchor": "#reset",
        "name": "Disable (DECRST)",
        "meaning": "CSI ? 12 l turns OFF blinking, giving a steady cursor.",
        "required": true,
        "byte_sequence_ST": "\u001b[?12l",
        "byte_sequence_ST_readable": "ESC [ ? 1 2 l   ==  \\x1b[?12l   (reset / DECRST)",
        "subparams": []
      }
    ],
    "gotchas": [
      "Mode 12 controls BLINK ONLY; the cursor SHAPE (block/underline/bar) comes from DECSCUSR (CSI Ps SP q). The two interact: DECSCUSR's odd values also imply blink, so they can fight mode 12.",
      "This is the 'att610' (AT&T 610) blink convention; not all terminals map mode 12 the same way, and some honor only DECSCUSR.",
      "Some terminals invert the meaning or ignore mode 12 in favor of a user preference for cursor blink.",
      "Restore the user's preferred blink state on exit rather than forcing it.",
      "Cursor blink is sometimes globally disabled by the OS/terminal for accessibility; your ?12h may have no visible effect."
    ],
    "v1_smoke_test": {
      "asserts": "Cursor-blink set/reset (?12h / ?12l) render as byte-exact DEC-private-mode sequences; blink-vs-shape (DECSCUSR) interaction recorded.",
      "behavioral_conformance": "deferred to v2."
    }
  },
  "updated": "2026-05-29T00:00:00Z"
}