FA-7841 / Keyboard accessibility / Open access
Sequential keyboard focus: Programmatic-only targets join sequential navigation · case 01
Programmatic-only targets join sequential navigation.
ROOT CAUSE
The negative operation uses `True` where the contract requires `item['tab'] >= 0`.
VERIFIED REPAIR
Implement the negative operation as `item['tab'] >= 0`.
Unsuccessful approach: Requiring positive tabindex excludes ordinary zero tabindex controls.
Case contract
Visit visible enabled nonnegative tabindex controls; positive tabindex precedes zero; ties retain document order and navigation wraps.
Why this case matters
A deterministic model of sequential keyboard focus; this isolates one interface invariant without requiring a browser.
1 / The failure
Exit 1"""Failure Map reference implementation. Python standard library only."""
import json
N = 1
observations = []
def solve(items, current, direction):
eligible = [i for i, item in enumerate(items) if item['visible'] and not item['disabled'] and True]
eligible.sort(key=lambda i: (items[i]['tab'] == 0, items[i]['tab'] if items[i]['tab'] > 0 else 0, i))
if not eligible: return None
if current not in eligible: return eligible[0] if direction > 0 else eligible[-1]
return eligible[(eligible.index(current) + direction) % len(eligible)]
def check(label, actual, expected):
observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('hidden', solve([dict(visible=False, disabled=False, tab=0),dict(visible=True,disabled=False,tab=0)], None, 1), 1)
check('disabled', solve([dict(visible=True,disabled=True,tab=0),dict(visible=True,disabled=False,tab=0)], None, 1), 1)
check('negative', solve([dict(visible=True,disabled=False,tab=-1),dict(visible=True,disabled=False,tab=0)], None, 1), 1)
check('priority', solve([dict(visible=True,disabled=False,tab=0),dict(visible=True,disabled=False,tab=2)], None, 1), 1)
check('reverse', solve([dict(visible=True,disabled=False,tab=0)]*3, 1, -1), 0)
check('forward', solve([dict(visible=True,disabled=False,tab=0)]*3, 1, 1), 2)
check('empty', solve([], None, 1), None)
check('parameterized focus sequence', solve([dict(visible=True, disabled=False, tab=0)]*(N+2), N, 1), N+1)
for repetition in range(N):
check('repeat empty', solve([], None, 1), None)
print(json.dumps({"observations": observations, "passed": all(x["passed"] for x in observations)}, ensure_ascii=False))
raise SystemExit(0 if all(x["passed"] for x in observations) else 1)
| Boundary fixture | Actual | Expected | Outcome |
|---|---|---|---|
| hidden | 1 | 1 | Passed |
| disabled | 1 | 1 | Passed |
| negative | 0 | 1 | Failed |
| priority | 1 | 1 | Passed |
| reverse | 0 | 0 | Passed |
| forward | 2 | 2 | Passed |
| empty | None | None | Passed |
| parameterized focus sequence | 2 | 2 | Passed |
| repeat empty | None | None | Passed |
SHA-256 / 7130c93809bff4a707b884466b983be6e5d8f36310f88262be93090614486464
2 / The unsuccessful fix
Exit 1"""Failure Map reference implementation. Python standard library only."""
import json
N = 1
observations = []
def solve(items, current, direction):
eligible = [i for i, item in enumerate(items) if item['visible'] and not item['disabled'] and item['tab'] > 0]
eligible.sort(key=lambda i: (items[i]['tab'] == 0, items[i]['tab'] if items[i]['tab'] > 0 else 0, i))
if not eligible: return None
if current not in eligible: return eligible[0] if direction > 0 else eligible[-1]
return eligible[(eligible.index(current) + direction) % len(eligible)]
def check(label, actual, expected):
observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('hidden', solve([dict(visible=False, disabled=False, tab=0),dict(visible=True,disabled=False,tab=0)], None, 1), 1)
check('disabled', solve([dict(visible=True,disabled=True,tab=0),dict(visible=True,disabled=False,tab=0)], None, 1), 1)
check('negative', solve([dict(visible=True,disabled=False,tab=-1),dict(visible=True,disabled=False,tab=0)], None, 1), 1)
check('priority', solve([dict(visible=True,disabled=False,tab=0),dict(visible=True,disabled=False,tab=2)], None, 1), 1)
check('reverse', solve([dict(visible=True,disabled=False,tab=0)]*3, 1, -1), 0)
check('forward', solve([dict(visible=True,disabled=False,tab=0)]*3, 1, 1), 2)
check('empty', solve([], None, 1), None)
check('parameterized focus sequence', solve([dict(visible=True, disabled=False, tab=0)]*(N+2), N, 1), N+1)
for repetition in range(N):
check('repeat empty', solve([], None, 1), None)
print(json.dumps({"observations": observations, "passed": all(x["passed"] for x in observations)}, ensure_ascii=False))
raise SystemExit(0 if all(x["passed"] for x in observations) else 1)
| Boundary fixture | Actual | Expected | Outcome |
|---|---|---|---|
| hidden | None | 1 | Failed |
| disabled | None | 1 | Failed |
| negative | None | 1 | Failed |
| priority | 1 | 1 | Passed |
| reverse | None | 0 | Failed |
| forward | None | 2 | Failed |
| empty | None | None | Passed |
| parameterized focus sequence | None | 2 | Failed |
| repeat empty | None | None | Passed |
SHA-256 / e371431de6ad2cd7f8d612e2db4a53085f30bafaf854c76822fb9de79f0eae99
3 / The verified repair
Exit 0"""Failure Map reference implementation. Python standard library only."""
import json
N = 1
observations = []
def solve(items, current, direction):
eligible = [i for i, item in enumerate(items) if item['visible'] and not item['disabled'] and item['tab'] >= 0]
eligible.sort(key=lambda i: (items[i]['tab'] == 0, items[i]['tab'] if items[i]['tab'] > 0 else 0, i))
if not eligible: return None
if current not in eligible: return eligible[0] if direction > 0 else eligible[-1]
return eligible[(eligible.index(current) + direction) % len(eligible)]
def check(label, actual, expected):
observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('hidden', solve([dict(visible=False, disabled=False, tab=0),dict(visible=True,disabled=False,tab=0)], None, 1), 1)
check('disabled', solve([dict(visible=True,disabled=True,tab=0),dict(visible=True,disabled=False,tab=0)], None, 1), 1)
check('negative', solve([dict(visible=True,disabled=False,tab=-1),dict(visible=True,disabled=False,tab=0)], None, 1), 1)
check('priority', solve([dict(visible=True,disabled=False,tab=0),dict(visible=True,disabled=False,tab=2)], None, 1), 1)
check('reverse', solve([dict(visible=True,disabled=False,tab=0)]*3, 1, -1), 0)
check('forward', solve([dict(visible=True,disabled=False,tab=0)]*3, 1, 1), 2)
check('empty', solve([], None, 1), None)
check('parameterized focus sequence', solve([dict(visible=True, disabled=False, tab=0)]*(N+2), N, 1), N+1)
for repetition in range(N):
check('repeat empty', solve([], None, 1), None)
print(json.dumps({"observations": observations, "passed": all(x["passed"] for x in observations)}, ensure_ascii=False))
raise SystemExit(0 if all(x["passed"] for x in observations) else 1)
| Boundary fixture | Actual | Expected | Outcome |
|---|---|---|---|
| hidden | 1 | 1 | Passed |
| disabled | 1 | 1 | Passed |
| negative | 1 | 1 | Passed |
| priority | 1 | 1 | Passed |
| reverse | 0 | 0 | Passed |
| forward | 2 | 2 | Passed |
| empty | None | None | Passed |
| parameterized focus sequence | 2 | 2 | Passed |
| repeat empty | None | None | Passed |
SHA-256 / b57c62a1fcaf2d8083d523782e366fd00a799e24974a856b307d0486e8c13a14
Verification & scope
This reproducer isolates one failure mechanism. Results cover the supplied fixtures. Variants within a family share a test contract and should remain grouped when constructing evaluation splits. Related mechanisms with a shared evaluation_group must also remain together; these controlled models are not independent production incidents.
Observations recorded using Python 3.12.14 at 2026-09-29T14:38:15.782671+00:00.
Case digest / 6852dbd8206bcd40651d44eb2ba992a7b9cf4737483b7604a8e22d271f5e0c80