FA-7856 / Keyboard accessibility / Open access

Modal focus restoration: Nested dialogs erase the outer return target · case 01

Nested dialogs erase the outer return target.

Verified by executionVariant 1 · 9 checks per implementationDownload source bundle ↓JSON ↗

ROOT CAUSE

The push operation uses `[target]` where the contract requires `stack + [target]`.

VERIFIED REPAIR

Implement the push operation as `stack + [target]`.

Unsuccessful approach: Prepending makes the oldest target appear newest.

Case contract

Opening pushes one return target; closing or Escape pops one scope; restoration chooses the newest connected target; clear empties the stack.

Why this case matters

A deterministic model of modal focus restoration; 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(stack, event, target, connected):
    stack = list(stack)
    if event == 'open': return [target]
    if event == 'close': return stack[:-1]
    if event == 'restore': return next((x for x in reversed(stack) if x in connected), None)
    if event == 'escape': return stack[:-1] if stack else []
    if event == 'clear': return []
    return stack
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('nested open', solve(['outer'], 'open', 'inner', []), ['outer', 'inner'])
check('nested close', solve(['outer','inner'], 'close', None, []), ['outer'])
check('newest live', solve(['z','a'], 'restore', None, ['z','a']), 'a')
check('ordered newest', solve(['a','z'], 'restore', None, ['a','z']), 'z')
check('detached', solve(['outer','gone'], 'restore', None, ['outer']), 'outer')
check('escape one', solve(['outer','inner'], 'escape', None, []), ['outer'])
check('clear', solve(['outer'], 'clear', None, []), [])
check('parameterized opener', solve(['outer'], 'open', 'dialog'+str(N), []), ['outer', 'dialog'+str(N)])
for repetition in range(N):
    check('repeat clear', solve(['outer'], 'clear', 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
nested open	`['inner']`	`['outer', 'inner']`	Failed
nested close	`['outer']`	`['outer']`	Passed
newest live	`a`	`a`	Passed
ordered newest	`z`	`z`	Passed
detached	`outer`	`outer`	Passed
escape one	`['outer']`	`['outer']`	Passed
clear	`[]`	`[]`	Passed
parameterized opener	`['dialog1']`	`['outer', 'dialog1']`	Failed
repeat clear	`[]`	`[]`	Passed

SHA-256 / 12cbad0b0d9fdecd59db57642f21aa874d77a42bba3108a55e6c7c36c80be72b

2 / The unsuccessful fix

Exit 1

"""Failure Map reference implementation. Python standard library only."""
import json

N = 1
observations = []
def solve(stack, event, target, connected):
    stack = list(stack)
    if event == 'open': return [target] + stack
    if event == 'close': return stack[:-1]
    if event == 'restore': return next((x for x in reversed(stack) if x in connected), None)
    if event == 'escape': return stack[:-1] if stack else []
    if event == 'clear': return []
    return stack
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('nested open', solve(['outer'], 'open', 'inner', []), ['outer', 'inner'])
check('nested close', solve(['outer','inner'], 'close', None, []), ['outer'])
check('newest live', solve(['z','a'], 'restore', None, ['z','a']), 'a')
check('ordered newest', solve(['a','z'], 'restore', None, ['a','z']), 'z')
check('detached', solve(['outer','gone'], 'restore', None, ['outer']), 'outer')
check('escape one', solve(['outer','inner'], 'escape', None, []), ['outer'])
check('clear', solve(['outer'], 'clear', None, []), [])
check('parameterized opener', solve(['outer'], 'open', 'dialog'+str(N), []), ['outer', 'dialog'+str(N)])
for repetition in range(N):
    check('repeat clear', solve(['outer'], 'clear', 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
nested open	`['inner', 'outer']`	`['outer', 'inner']`	Failed
nested close	`['outer']`	`['outer']`	Passed
newest live	`a`	`a`	Passed
ordered newest	`z`	`z`	Passed
detached	`outer`	`outer`	Passed
escape one	`['outer']`	`['outer']`	Passed
clear	`[]`	`[]`	Passed
parameterized opener	`['dialog1', 'outer']`	`['outer', 'dialog1']`	Failed
repeat clear	`[]`	`[]`	Passed

SHA-256 / 7614f006979f3dd8a57830372591fae48efeeb2677a1c3fa10c9e65bd3a45c1a

3 / The verified repair

Exit 0

"""Failure Map reference implementation. Python standard library only."""
import json

N = 1
observations = []
def solve(stack, event, target, connected):
    stack = list(stack)
    if event == 'open': return stack + [target]
    if event == 'close': return stack[:-1]
    if event == 'restore': return next((x for x in reversed(stack) if x in connected), None)
    if event == 'escape': return stack[:-1] if stack else []
    if event == 'clear': return []
    return stack
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('nested open', solve(['outer'], 'open', 'inner', []), ['outer', 'inner'])
check('nested close', solve(['outer','inner'], 'close', None, []), ['outer'])
check('newest live', solve(['z','a'], 'restore', None, ['z','a']), 'a')
check('ordered newest', solve(['a','z'], 'restore', None, ['a','z']), 'z')
check('detached', solve(['outer','gone'], 'restore', None, ['outer']), 'outer')
check('escape one', solve(['outer','inner'], 'escape', None, []), ['outer'])
check('clear', solve(['outer'], 'clear', None, []), [])
check('parameterized opener', solve(['outer'], 'open', 'dialog'+str(N), []), ['outer', 'dialog'+str(N)])
for repetition in range(N):
    check('repeat clear', solve(['outer'], 'clear', 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
nested open	`['outer', 'inner']`	`['outer', 'inner']`	Passed
nested close	`['outer']`	`['outer']`	Passed
newest live	`a`	`a`	Passed
ordered newest	`z`	`z`	Passed
detached	`outer`	`outer`	Passed
escape one	`['outer']`	`['outer']`	Passed
clear	`[]`	`[]`	Passed
parameterized opener	`['outer', 'dialog1']`	`['outer', 'dialog1']`	Passed
repeat clear	`[]`	`[]`	Passed

SHA-256 / 8901a8b8c65cfc32a871a684954e66a19f6e67cb2db84f1b471e3d704b7c9981

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 2026-09-29T14:38:15.961875+00:00.

Case digest / 03601a13bd2de49da97ba8fac63232d5041e59b8ac729f72984b863c6ff50ee5