FA-54736 / Accessibility interaction semantics / Open access

Visual line indices are one-based in a zero-based API · case 01

Visual line indices are one-based in a zero-based API.

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

ROOT CAUSE

The line ordinal decision in the visual line query adapter violates its declared contract.

THE FAILURE

The line ordinal decision in the visual line query adapter violates its declared contract.

Unsuccessful approach: The local repair substitutes return [max(1,index),start,end but still mishandles the regression fixtures.

Case contract

Input [text,lines,offset,affinity] lines ordered nonoverlapping [start,end,hard_break] in codepoint coordinates. Each line covers half-open text range; an offset on shared line boundary selects next line for forward affinity, previous for backward. Final document-end offset selects final line. Empty text with one empty line is valid. Return [index,start,end,text_segment,hard_break], or None for offsets outside text or gaps. Newline characters are included only if line bounds include them. No text wrapping is performed.

Why this case matters

Offline accessibility bridge model with explicit policy; useful for testing semantic API adapters independently of browser implementations.

1 / The failure

Exit 1

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

N = 1
observations = []
def solve(data):
    text,lines,offset,affinity = data
    if offset < 0 or offset > len(text): return None
    matches = []
    for i,(start,end,hard) in enumerate(lines):
        inside = start <= offset < end
        boundary = offset == end and (affinity == 'backward' or offset == len(text))
        empty = start == end == offset and len(text) == 0
        if inside or boundary or empty: matches.append(i)
    if not matches: return None
    index = matches[0] if affinity == 'backward' else matches[-1]
    start,end,hard = lines[index]
    return [index+1,start,end,text[start:end],hard]
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('contract fixture 1', solve(['A'*N+'BC',[[0,N,False],[N,N+2,True]],N,'forward'],), [1,N,N+2,'BC',True])
check('contract fixture 2', solve(['A'*N+'BC',[[0,N,False],[N,N+2,True]],N,'backward'],), [0,0,N,'A'*N,False])
check('contract fixture 3', solve(['abc',[[0,3,False]],3,'forward'],), [0,0,3,'abc',False])
check('contract fixture 4', solve(['a\nb',[[0,2,True],[2,3,False]],1,'forward'],), [0,0,2,'a\n',True])
check('contract fixture 5', solve(['abc',[[0,1,False],[2,3,False]],1,'forward'],), None)
check('contract fixture 6', solve(['abc',[[0,3,False]],-1,'backward'],), None)
check('contract fixture 7', solve(['abc',[[0,3,False]],4,'backward'],), None)
check('contract fixture 8', solve(['',[[0,0,False]],0,'forward'],), [0,0,0,'',False])
check('contract fixture 9', solve(['abc',[],0,'forward'],), 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
contract fixture 1	`[2, 1, 3, 'BC', True]`	`[1, 1, 3, 'BC', True]`	Failed
contract fixture 2	`[1, 0, 1, 'A', False]`	`[0, 0, 1, 'A', False]`	Failed
contract fixture 3	`[1, 0, 3, 'abc', False]`	`[0, 0, 3, 'abc', False]`	Failed
contract fixture 4	`[1, 0, 2, 'a\n', True]`	`[0, 0, 2, 'a\n', True]`	Failed
contract fixture 5	`None`	`None`	Passed
contract fixture 6	`None`	`None`	Passed
contract fixture 7	`None`	`None`	Passed
contract fixture 8	`[1, 0, 0, '', False]`	`[0, 0, 0, '', False]`	Failed
contract fixture 9	`None`	`None`	Passed

SHA-256 / b5ecb68e5a0b5a132fc72599c5f46f61ea7124ef6826f559e1048690e0621ad5

2 / The unsuccessful fix

Exit 1

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

N = 1
observations = []
def solve(data):
    text,lines,offset,affinity = data
    if offset < 0 or offset > len(text): return None
    matches = []
    for i,(start,end,hard) in enumerate(lines):
        inside = start <= offset < end
        boundary = offset == end and (affinity == 'backward' or offset == len(text))
        empty = start == end == offset and len(text) == 0
        if inside or boundary or empty: matches.append(i)
    if not matches: return None
    index = matches[0] if affinity == 'backward' else matches[-1]
    start,end,hard = lines[index]
    return [max(1,index),start,end,text[start:end],hard]
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('contract fixture 1', solve(['A'*N+'BC',[[0,N,False],[N,N+2,True]],N,'forward'],), [1,N,N+2,'BC',True])
check('contract fixture 2', solve(['A'*N+'BC',[[0,N,False],[N,N+2,True]],N,'backward'],), [0,0,N,'A'*N,False])
check('contract fixture 3', solve(['abc',[[0,3,False]],3,'forward'],), [0,0,3,'abc',False])
check('contract fixture 4', solve(['a\nb',[[0,2,True],[2,3,False]],1,'forward'],), [0,0,2,'a\n',True])
check('contract fixture 5', solve(['abc',[[0,1,False],[2,3,False]],1,'forward'],), None)
check('contract fixture 6', solve(['abc',[[0,3,False]],-1,'backward'],), None)
check('contract fixture 7', solve(['abc',[[0,3,False]],4,'backward'],), None)
check('contract fixture 8', solve(['',[[0,0,False]],0,'forward'],), [0,0,0,'',False])
check('contract fixture 9', solve(['abc',[],0,'forward'],), 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
contract fixture 1	`[1, 1, 3, 'BC', True]`	`[1, 1, 3, 'BC', True]`	Passed
contract fixture 2	`[1, 0, 1, 'A', False]`	`[0, 0, 1, 'A', False]`	Failed
contract fixture 3	`[1, 0, 3, 'abc', False]`	`[0, 0, 3, 'abc', False]`	Failed
contract fixture 4	`[1, 0, 2, 'a\n', True]`	`[0, 0, 2, 'a\n', True]`	Failed
contract fixture 5	`None`	`None`	Passed
contract fixture 6	`None`	`None`	Passed
contract fixture 7	`None`	`None`	Passed
contract fixture 8	`[1, 0, 0, '', False]`	`[0, 0, 0, '', False]`	Failed
contract fixture 9	`None`	`None`	Passed

SHA-256 / 98b212712bce90d1519343b7be7b2dc58d48f991bfe9cabaa8f82e20288d9491

HELD IN THE MEMBER ARCHIVE

The verified repair and its recorded checks are member-only.

This mechanism has 9 recorded checks per implementation. The open-access tier publishes the failure and the unsuccessful fix; the repaired source that passes every check, and the observations that prove it, are available to members.

Every case sharing this mechanism uses the same contract and the same repair, so this one record is held back for all of them.

Member access is invitation-based. Sign in with your invited account to inspect the repair.

Verification & scope

Stipulated finite adapter contract, not a claim of platform accessibility or ARIA conformance. 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 2026-09-29T14:45:51.148461+00:00.

Case digest / 3e28d2d1f3ded6d0403ddd2b5dcf9d35c56a2b8c3bcf3c558d275b43e258bb4f