{
  "id": "terminal-dec-private-mode/1",
  "family": "terminal-dec-private-mode",
  "slug": "1",
  "title": "DECSET 1 — DECCKM (application cursor keys)",
  "summary": "CSI ? 1 h (DECCKM set) switches the cursor (arrow) keys into 'application' mode: they send SS3-prefixed sequences (ESC O A/B/C/D) instead of the normal CSI forms (ESC [ A/B/C/D). CSI ? 1 l restores normal mode. Full-screen programs enable it so arrow keys are unambiguous.",
  "kind": "control-sequence",
  "aliases": [
    "DECCKM",
    "application cursor keys",
    "DECSET 1",
    "?1h / ?1l",
    "cursor key mode"
  ],
  "status": "standard",
  "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 -> Application Cursor Keys (DECCKM). When set, cursor keys send ESC O x (SS3) instead of ESC [ x."
    },
    {
      "claim_ref": "ext.params",
      "source_url": "https://vt100.net/docs/vt510-rm/DECCKM.html",
      "source_version": "DEC VT510 Programmer Reference, DECCKM, retrieved 2026-05-29",
      "note": "DEC VT510 manual: DECCKM (mode 1) selects application vs normal cursor-key sequences."
    }
  ],
  "see_also": [
    "terminal-dec-private-mode/1004"
  ],
  "ext_type": "terminal-escape@1",
  "ext": {
    "csi_or_osc": "DEC-private-mode",
    "command_number": 1,
    "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 ? 1 h sets DECCKM: arrow keys now send SS3 sequences, e.g. Up = ESC O A (\\x1bOA) rather than ESC [ A.",
        "required": true,
        "byte_sequence_ST": "\u001b[?1h",
        "byte_sequence_ST_readable": "ESC [ ? 1 h   ==  \\x1b[?1h   (set / DECSET)",
        "subparams": []
      },
      {
        "id": "reset",
        "anchor": "#reset",
        "name": "Disable (DECRST)",
        "meaning": "CSI ? 1 l clears DECCKM: arrow keys send the normal CSI sequences ESC [ A/B/C/D.",
        "required": true,
        "byte_sequence_ST": "\u001b[?1l",
        "byte_sequence_ST_readable": "ESC [ ? 1 l   ==  \\x1b[?1l   (reset / DECRST)",
        "subparams": []
      }
    ],
    "gotchas": [
      "In APPLICATION mode arrow keys are ESC O A..D (SS3); in NORMAL mode they are ESC [ A..D (CSI). A key-parser must know the current mode or read both.",
      "Many TUIs enable DECCKM via terminfo (smkx) on entry and disable it (rmkx) on exit; if your program crashes without resetting, the shell's arrow keys can misbehave until reset.",
      "DECCKM affects only the cursor (arrow) keys, not the numeric keypad (that is DECKPAM/DECKPNM).",
      "The SS3 prefix is ESC O (0x1B 0x4F), not ESC [ — easy to confuse when matching byte patterns.",
      "Always pair set on entry with reset on exit (or rely on terminfo smkx/rmkx)."
    ],
    "v1_smoke_test": {
      "asserts": "DECCKM set/reset (?1h / ?1l) render as byte-exact DEC-private-mode sequences; SS3-vs-CSI arrow-key effect recorded.",
      "behavioral_conformance": "deferred to v2."
    }
  },
  "updated": "2026-05-29T00:00:00Z"
}