{"abstract":"Clicking the right half of an RTL character places the caret after it logically.","category":"Bidirectional text layout","checks":8,"contract":"Input [levels, x in half-character units]. Clamp to a visual slot (each character 2 units). The right half of an LTR character or the left half of an RTL character is its trailing side. Points before the line use the left half of slot 0, beyond it the right half of the last slot. Return [logical index, trailing, caret offset].","evaluation_group":"w2-bidirectional-text-layout-hit-testing","failed_approach":"Clearing trailing for all RTL characters is also wrong.","family":"w2-bidirectional-text-layout-hit-testing-trailing-side-for-rtl","id":"FA-80691","implementations":{"attempt":{"sha256":"38f6fb7c2e5dd03cabecd2da2c3755493e82c534b329720b08af13d490a65456","source":"\"\"\"Failure Map reference implementation. Python standard library only.\"\"\"\nimport json\n\nN = 1\nobservations = []\ndef solve(x):\n    def reorder(lv):\n        vis = list(range(len(lv)))\n        odd = [l for l in lv if l % 2 == 1]\n        if not odd:\n            return vis\n        for lev in range(max(lv), min(odd) - 1, -1):\n            i = 0\n            while i < len(vis):\n                if lv[vis[i]] >= lev:\n                    j = i\n                    while j < len(vis) and lv[vis[j]] >= lev:\n                        j += 1\n                    vis[i:j] = vis[i:j][::-1]\n                    i = j\n                else:\n                    i += 1\n        return vis\n    \n    levels, px = x\n    n = len(levels)\n    if n == 0:\n        return [None, False, 0]\n    vis = reorder(levels)\n    v = min(max(px // 2, 0), n - 1)\n    i = vis[v]\n    right_half = px - 2 * v >= 1\n    rtl = levels[i] % 2 == 1\n    trailing = right_half and not rtl\n    return [i, trailing, i + 1 if trailing else i]\ndef check(label, actual, expected):\n    observations.append({\"check\": label, \"actual\": actual, \"expected\": expected, \"passed\": actual == expected})\nfixtures = [[('click left of RTL line', [[1, 1, 1], -1], [2, True, 3]), ('regression: trailing side for RTL', [[1, 1, 1, 1, 1, 1, 0, 0, 3], 6], [2, True, 3]), ('regression: trailing side for RTL', [[3, 3, 3, 2, 2, 2, 2, 0, 0], 0], [2, True, 3]), ('regression: trailing side for RTL', [[1, 1, 1, 1, 4, 4, 4, 4, 3], -3], [8, True, 9]), ('right half of RTL char', [[1, 1], 1], [1, False, 1]), ('click past end', [[0, 1, 1], 9], [1, False, 1]), ('control layout', [[2, 2, 3, 3, 1, 1, 1], 8], [1, False, 1]), ('control layout', [[0], 1], [0, True, 1])], [('regression: trailing side for RTL', [[1, 1, 1, 3, 3, 3, 3, 2, 3], 11], [8, False, 8]), ('regression: trailing side for RTL', [[0, 0, 2, 3, 3, 3, 3, 3], 19], [3, False, 3]), ('regression: trailing side for RTL', [[3, 3, 3, 3, 4, 4, 4, 1], 8], [3, True, 4]), ('regression: trailing side for RTL', [[2, 2, 2, 3, 3, 3], 6], [5, True, 6]), ('right half of RTL char', [[1, 1], 1], [1, False, 1]), ('click past end', [[0, 1, 1], 9], [1, False, 1]), ('control layout', [[0, 0, 0, 0, 2, 2], 15], [5, True, 6]), ('control layout', [[1, 1, 0], 7], [2, True, 3])], [('regression: trailing side for RTL', [[1, 1, 2, 3], 2], [3, True, 4]), ('right half of RTL char', [[1, 1], 1], [1, False, 1]), ('regression: trailing side for RTL', [[1, 1, 1, 0, 3, 3, 3, 3, 0, 0], 14], [4, True, 5]), ('regression: trailing side for RTL', [[1, 1, 1, 1], -1], [3, True, 4]), ('click past end', [[0, 1, 1], 9], [1, False, 1]), ('click left of RTL line', [[1, 1, 1], -1], [2, True, 3]), ('control layout', [[2, 2, 2, 1, 1, 3, 1], 11], [1, True, 2]), ('control layout', [[0, 0, 0, 1], 0], [0, False, 0])], [('regression: trailing side for RTL', [[3, 3, 3, 3, 3, 3, 2, 2, 2, 2], 1], [5, False, 5]), ('regression: trailing side for RTL', [[2, 2, 2, 2, 2, 2, 3, 3], 17], [6, False, 6]), ('regression: trailing side for RTL', [[3, 3, 3, 3, 3, 3, 3], 6], [3, True, 4]), ('regression: trailing side for RTL', [[1, 1], -1], [1, True, 2]), ('right half of RTL char', [[1, 1], 1], [1, False, 1]), ('click left of RTL line', [[1, 1, 1], -1], [2, True, 3]), ('control layout', [[1, 2, 2], 1], [1, True, 2]), ('control layout', [[4, 4], -2], [0, False, 0])], [('regression: trailing side for RTL', [[2, 2, 2, 1, 1], -3], [4, True, 5]), ('regression: trailing side for RTL', [[3, 3, 3, 3, 2, 2, 2, 2, 1, 1], 4], [3, True, 4]), ('regression: trailing side for RTL', [[1, 0, 3, 3, 3, 3, 3, 3, 3], -2], [0, True, 1]), ('regression: trailing side for RTL', [[1, 1], 0], [1, True, 2]), ('click past end', [[0, 1, 1], 9], [1, False, 1]), ('right half of RTL char', [[1, 1], 1], [1, False, 1]), ('control layout', [[4], 4], [0, True, 1]), ('control layout', [[2, 2, 2, 2, 2, 2, 2, 1, 1, 1], 16], [5, False, 5])]]\nfor label, args, expected in fixtures[N - 1]:\n    check(label, solve(args), expected)\nprint(json.dumps({\"observations\": observations, \"passed\": all(x[\"passed\"] for x in observations)}, ensure_ascii=False))\nraise SystemExit(0 if all(x[\"passed\"] for x in observations) else 1)\n"},"broken":{"sha256":"d08fc0c799ea01260b46713b6ed0aaa734e1fb27a13cadfe76281c6c2199b8e6","source":"\"\"\"Failure Map reference implementation. Python standard library only.\"\"\"\nimport json\n\nN = 1\nobservations = []\ndef solve(x):\n    def reorder(lv):\n        vis = list(range(len(lv)))\n        odd = [l for l in lv if l % 2 == 1]\n        if not odd:\n            return vis\n        for lev in range(max(lv), min(odd) - 1, -1):\n            i = 0\n            while i < len(vis):\n                if lv[vis[i]] >= lev:\n                    j = i\n                    while j < len(vis) and lv[vis[j]] >= lev:\n                        j += 1\n                    vis[i:j] = vis[i:j][::-1]\n                    i = j\n                else:\n                    i += 1\n        return vis\n    \n    levels, px = x\n    n = len(levels)\n    if n == 0:\n        return [None, False, 0]\n    vis = reorder(levels)\n    v = min(max(px // 2, 0), n - 1)\n    i = vis[v]\n    right_half = px - 2 * v >= 1\n    rtl = levels[i] % 2 == 1\n    trailing = right_half\n    return [i, trailing, i + 1 if trailing else i]\ndef check(label, actual, expected):\n    observations.append({\"check\": label, \"actual\": actual, \"expected\": expected, \"passed\": actual == expected})\nfixtures = [[('click left of RTL line', [[1, 1, 1], -1], [2, True, 3]), ('regression: trailing side for RTL', [[1, 1, 1, 1, 1, 1, 0, 0, 3], 6], [2, True, 3]), ('regression: trailing side for RTL', [[3, 3, 3, 2, 2, 2, 2, 0, 0], 0], [2, True, 3]), ('regression: trailing side for RTL', [[1, 1, 1, 1, 4, 4, 4, 4, 3], -3], [8, True, 9]), ('right half of RTL char', [[1, 1], 1], [1, False, 1]), ('click past end', [[0, 1, 1], 9], [1, False, 1]), ('control layout', [[2, 2, 3, 3, 1, 1, 1], 8], [1, False, 1]), ('control layout', [[0], 1], [0, True, 1])], [('regression: trailing side for RTL', [[1, 1, 1, 3, 3, 3, 3, 2, 3], 11], [8, False, 8]), ('regression: trailing side for RTL', [[0, 0, 2, 3, 3, 3, 3, 3], 19], [3, False, 3]), ('regression: trailing side for RTL', [[3, 3, 3, 3, 4, 4, 4, 1], 8], [3, True, 4]), ('regression: trailing side for RTL', [[2, 2, 2, 3, 3, 3], 6], [5, True, 6]), ('right half of RTL char', [[1, 1], 1], [1, False, 1]), ('click past end', [[0, 1, 1], 9], [1, False, 1]), ('control layout', [[0, 0, 0, 0, 2, 2], 15], [5, True, 6]), ('control layout', [[1, 1, 0], 7], [2, True, 3])], [('regression: trailing side for RTL', [[1, 1, 2, 3], 2], [3, True, 4]), ('right half of RTL char', [[1, 1], 1], [1, False, 1]), ('regression: trailing side for RTL', [[1, 1, 1, 0, 3, 3, 3, 3, 0, 0], 14], [4, True, 5]), ('regression: trailing side for RTL', [[1, 1, 1, 1], -1], [3, True, 4]), ('click past end', [[0, 1, 1], 9], [1, False, 1]), ('click left of RTL line', [[1, 1, 1], -1], [2, True, 3]), ('control layout', [[2, 2, 2, 1, 1, 3, 1], 11], [1, True, 2]), ('control layout', [[0, 0, 0, 1], 0], [0, False, 0])], [('regression: trailing side for RTL', [[3, 3, 3, 3, 3, 3, 2, 2, 2, 2], 1], [5, False, 5]), ('regression: trailing side for RTL', [[2, 2, 2, 2, 2, 2, 3, 3], 17], [6, False, 6]), ('regression: trailing side for RTL', [[3, 3, 3, 3, 3, 3, 3], 6], [3, True, 4]), ('regression: trailing side for RTL', [[1, 1], -1], [1, True, 2]), ('right half of RTL char', [[1, 1], 1], [1, False, 1]), ('click left of RTL line', [[1, 1, 1], -1], [2, True, 3]), ('control layout', [[1, 2, 2], 1], [1, True, 2]), ('control layout', [[4, 4], -2], [0, False, 0])], [('regression: trailing side for RTL', [[2, 2, 2, 1, 1], -3], [4, True, 5]), ('regression: trailing side for RTL', [[3, 3, 3, 3, 2, 2, 2, 2, 1, 1], 4], [3, True, 4]), ('regression: trailing side for RTL', [[1, 0, 3, 3, 3, 3, 3, 3, 3], -2], [0, True, 1]), ('regression: trailing side for RTL', [[1, 1], 0], [1, True, 2]), ('click past end', [[0, 1, 1], 9], [1, False, 1]), ('right half of RTL char', [[1, 1], 1], [1, False, 1]), ('control layout', [[4], 4], [0, True, 1]), ('control layout', [[2, 2, 2, 2, 2, 2, 2, 1, 1, 1], 16], [5, False, 5])]]\nfor label, args, expected in fixtures[N - 1]:\n    check(label, solve(args), expected)\nprint(json.dumps({\"observations\": observations, \"passed\": all(x[\"passed\"] for x in observations)}, ensure_ascii=False))\nraise SystemExit(0 if all(x[\"passed\"] for x in observations) else 1)\n"},"fixed":{"sha256":"690902346e54d7e6219a886a259210e3821de631cbfe1184d0f878a18230b4fd","source":"\"\"\"Failure Map reference implementation. Python standard library only.\"\"\"\nimport json\n\nN = 1\nobservations = []\ndef solve(x):\n    def reorder(lv):\n        vis = list(range(len(lv)))\n        odd = [l for l in lv if l % 2 == 1]\n        if not odd:\n            return vis\n        for lev in range(max(lv), min(odd) - 1, -1):\n            i = 0\n            while i < len(vis):\n                if lv[vis[i]] >= lev:\n                    j = i\n                    while j < len(vis) and lv[vis[j]] >= lev:\n                        j += 1\n                    vis[i:j] = vis[i:j][::-1]\n                    i = j\n                else:\n                    i += 1\n        return vis\n    \n    levels, px = x\n    n = len(levels)\n    if n == 0:\n        return [None, False, 0]\n    vis = reorder(levels)\n    v = min(max(px // 2, 0), n - 1)\n    i = vis[v]\n    right_half = px - 2 * v >= 1\n    rtl = levels[i] % 2 == 1\n    trailing = right_half != rtl\n    return [i, trailing, i + 1 if trailing else i]\ndef check(label, actual, expected):\n    observations.append({\"check\": label, \"actual\": actual, \"expected\": expected, \"passed\": actual == expected})\nfixtures = [[('click left of RTL line', [[1, 1, 1], -1], [2, True, 3]), ('regression: trailing side for RTL', [[1, 1, 1, 1, 1, 1, 0, 0, 3], 6], [2, True, 3]), ('regression: trailing side for RTL', [[3, 3, 3, 2, 2, 2, 2, 0, 0], 0], [2, True, 3]), ('regression: trailing side for RTL', [[1, 1, 1, 1, 4, 4, 4, 4, 3], -3], [8, True, 9]), ('right half of RTL char', [[1, 1], 1], [1, False, 1]), ('click past end', [[0, 1, 1], 9], [1, False, 1]), ('control layout', [[2, 2, 3, 3, 1, 1, 1], 8], [1, False, 1]), ('control layout', [[0], 1], [0, True, 1])], [('regression: trailing side for RTL', [[1, 1, 1, 3, 3, 3, 3, 2, 3], 11], [8, False, 8]), ('regression: trailing side for RTL', [[0, 0, 2, 3, 3, 3, 3, 3], 19], [3, False, 3]), ('regression: trailing side for RTL', [[3, 3, 3, 3, 4, 4, 4, 1], 8], [3, True, 4]), ('regression: trailing side for RTL', [[2, 2, 2, 3, 3, 3], 6], [5, True, 6]), ('right half of RTL char', [[1, 1], 1], [1, False, 1]), ('click past end', [[0, 1, 1], 9], [1, False, 1]), ('control layout', [[0, 0, 0, 0, 2, 2], 15], [5, True, 6]), ('control layout', [[1, 1, 0], 7], [2, True, 3])], [('regression: trailing side for RTL', [[1, 1, 2, 3], 2], [3, True, 4]), ('right half of RTL char', [[1, 1], 1], [1, False, 1]), ('regression: trailing side for RTL', [[1, 1, 1, 0, 3, 3, 3, 3, 0, 0], 14], [4, True, 5]), ('regression: trailing side for RTL', [[1, 1, 1, 1], -1], [3, True, 4]), ('click past end', [[0, 1, 1], 9], [1, False, 1]), ('click left of RTL line', [[1, 1, 1], -1], [2, True, 3]), ('control layout', [[2, 2, 2, 1, 1, 3, 1], 11], [1, True, 2]), ('control layout', [[0, 0, 0, 1], 0], [0, False, 0])], [('regression: trailing side for RTL', [[3, 3, 3, 3, 3, 3, 2, 2, 2, 2], 1], [5, False, 5]), ('regression: trailing side for RTL', [[2, 2, 2, 2, 2, 2, 3, 3], 17], [6, False, 6]), ('regression: trailing side for RTL', [[3, 3, 3, 3, 3, 3, 3], 6], [3, True, 4]), ('regression: trailing side for RTL', [[1, 1], -1], [1, True, 2]), ('right half of RTL char', [[1, 1], 1], [1, False, 1]), ('click left of RTL line', [[1, 1, 1], -1], [2, True, 3]), ('control layout', [[1, 2, 2], 1], [1, True, 2]), ('control layout', [[4, 4], -2], [0, False, 0])], [('regression: trailing side for RTL', [[2, 2, 2, 1, 1], -3], [4, True, 5]), ('regression: trailing side for RTL', [[3, 3, 3, 3, 2, 2, 2, 2, 1, 1], 4], [3, True, 4]), ('regression: trailing side for RTL', [[1, 0, 3, 3, 3, 3, 3, 3, 3], -2], [0, True, 1]), ('regression: trailing side for RTL', [[1, 1], 0], [1, True, 2]), ('click past end', [[0, 1, 1], 9], [1, False, 1]), ('right half of RTL char', [[1, 1], 1], [1, False, 1]), ('control layout', [[4], 4], [0, True, 1]), ('control layout', [[2, 2, 2, 2, 2, 2, 2, 1, 1, 1], 16], [5, False, 5])]]\nfor label, args, expected in fixtures[N - 1]:\n    check(label, solve(args), expected)\nprint(json.dumps({\"observations\": observations, \"passed\": all(x[\"passed\"] for x in observations)}, ensure_ascii=False))\nraise SystemExit(0 if all(x[\"passed\"] for x in observations) else 1)\n"}},"limitations":"A deterministic toy bidi model over stipulated class labels and integer levels; it is inspired by, but does not claim conformance to, any published algorithm. 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.","method":"Deterministic executable model with adversarial boundary fixtures.","provenance":{"created_by":"Failure Map","dependencies":"Python standard library","family":"w2-bidirectional-text-layout-hit-testing-trailing-side-for-rtl","generated_at":"2026-09-29T14:49:56.127010+00:00","license":"CC0-1.0","python":"3.12.14","seed":1,"split":"open-access"},"relevance":"Mixed right-to-left and left-to-right text must resolve levels and visual order exactly, or words, numbers and carets land in the wrong place.","repair":"Flip the half-to-edge mapping for RTL characters.","root_cause":"The trailing flag ignores the character direction.","sha256":"810a96e6e02586b8c0058a5d811ce70709849a08516816da1fd6de10197eca3b","title":"Bidi hit testing: trailing side for RTL · case 01","variant":1,"variant_policy":"Five numbered records share a model and may reuse boundary fixtures.","verification":{"attempt":{"elapsed_ms":41.325,"exit_code":1,"observations":[{"actual":[2,false,2],"check":"click left of RTL line","expected":[2,true,3],"passed":false},{"actual":[2,false,2],"check":"regression: trailing side for RTL","expected":[2,true,3],"passed":false},{"actual":[2,false,2],"check":"regression: trailing side for RTL","expected":[2,true,3],"passed":false},{"actual":[8,false,8],"check":"regression: trailing side for RTL","expected":[8,true,9],"passed":false},{"actual":[1,false,1],"check":"right half of RTL char","expected":[1,false,1],"passed":true},{"actual":[1,false,1],"check":"click past end","expected":[1,false,1],"passed":true},{"actual":[1,false,1],"check":"control layout","expected":[1,false,1],"passed":true},{"actual":[0,true,1],"check":"control layout","expected":[0,true,1],"passed":true}],"passed":false,"stderr":"","stdout":"{\"observations\": [{\"check\": \"click left of RTL line\", \"actual\": [2, false, 2], \"expected\": [2, true, 3], \"passed\": false}, {\"check\": \"regression: trailing side for RTL\", \"actual\": [2, false, 2], \"expected\": [2, true, 3], \"passed\": false}, {\"check\": \"regression: trailing side for RTL\", \"actual\": [2, false, 2], \"expected\": [2, true, 3], \"passed\": false}, {\"check\": \"regression: trailing side for RTL\", \"actual\": [8, false, 8], \"expected\": [8, true, 9], \"passed\": false}, {\"check\": \"right half of RTL char\", \"actual\": [1, false, 1], \"expected\": [1, false, 1], \"passed\": true}, {\"check\": \"click past end\", \"actual\": [1, false, 1], \"expected\": [1, false, 1], \"passed\": true}, {\"check\": \"control layout\", \"actual\": [1, false, 1], \"expected\": [1, false, 1], \"passed\": true}, {\"check\": \"control layout\", \"actual\": [0, true, 1], \"expected\": [0, true, 1], \"passed\": true}], \"passed\": false}\n"},"broken":{"elapsed_ms":38.293,"exit_code":1,"observations":[{"actual":[2,false,2],"check":"click left of RTL line","expected":[2,true,3],"passed":false},{"actual":[2,false,2],"check":"regression: trailing side for RTL","expected":[2,true,3],"passed":false},{"actual":[2,false,2],"check":"regression: trailing side for RTL","expected":[2,true,3],"passed":false},{"actual":[8,false,8],"check":"regression: trailing side for RTL","expected":[8,true,9],"passed":false},{"actual":[1,true,2],"check":"right half of RTL char","expected":[1,false,1],"passed":false},{"actual":[1,true,2],"check":"click past end","expected":[1,false,1],"passed":false},{"actual":[1,false,1],"check":"control layout","expected":[1,false,1],"passed":true},{"actual":[0,true,1],"check":"control layout","expected":[0,true,1],"passed":true}],"passed":false,"stderr":"","stdout":"{\"observations\": [{\"check\": \"click left of RTL line\", \"actual\": [2, false, 2], \"expected\": [2, true, 3], \"passed\": false}, {\"check\": \"regression: trailing side for RTL\", \"actual\": [2, false, 2], \"expected\": [2, true, 3], \"passed\": false}, {\"check\": \"regression: trailing side for RTL\", \"actual\": [2, false, 2], \"expected\": [2, true, 3], \"passed\": false}, {\"check\": \"regression: trailing side for RTL\", \"actual\": [8, false, 8], \"expected\": [8, true, 9], \"passed\": false}, {\"check\": \"right half of RTL char\", \"actual\": [1, true, 2], \"expected\": [1, false, 1], \"passed\": false}, {\"check\": \"click past end\", \"actual\": [1, true, 2], \"expected\": [1, false, 1], \"passed\": false}, {\"check\": \"control layout\", \"actual\": [1, false, 1], \"expected\": [1, false, 1], \"passed\": true}, {\"check\": \"control layout\", \"actual\": [0, true, 1], \"expected\": [0, true, 1], \"passed\": true}], \"passed\": false}\n"},"fixed":{"elapsed_ms":37.487,"exit_code":0,"observations":[{"actual":[2,true,3],"check":"click left of RTL line","expected":[2,true,3],"passed":true},{"actual":[2,true,3],"check":"regression: trailing side for RTL","expected":[2,true,3],"passed":true},{"actual":[2,true,3],"check":"regression: trailing side for RTL","expected":[2,true,3],"passed":true},{"actual":[8,true,9],"check":"regression: trailing side for RTL","expected":[8,true,9],"passed":true},{"actual":[1,false,1],"check":"right half of RTL char","expected":[1,false,1],"passed":true},{"actual":[1,false,1],"check":"click past end","expected":[1,false,1],"passed":true},{"actual":[1,false,1],"check":"control layout","expected":[1,false,1],"passed":true},{"actual":[0,true,1],"check":"control layout","expected":[0,true,1],"passed":true}],"passed":true,"stderr":"","stdout":"{\"observations\": [{\"check\": \"click left of RTL line\", \"actual\": [2, true, 3], \"expected\": [2, true, 3], \"passed\": true}, {\"check\": \"regression: trailing side for RTL\", \"actual\": [2, true, 3], \"expected\": [2, true, 3], \"passed\": true}, {\"check\": \"regression: trailing side for RTL\", \"actual\": [2, true, 3], \"expected\": [2, true, 3], \"passed\": true}, {\"check\": \"regression: trailing side for RTL\", \"actual\": [8, true, 9], \"expected\": [8, true, 9], \"passed\": true}, {\"check\": \"right half of RTL char\", \"actual\": [1, false, 1], \"expected\": [1, false, 1], \"passed\": true}, {\"check\": \"click past end\", \"actual\": [1, false, 1], \"expected\": [1, false, 1], \"passed\": true}, {\"check\": \"control layout\", \"actual\": [1, false, 1], \"expected\": [1, false, 1], \"passed\": true}, {\"check\": \"control layout\", \"actual\": [0, true, 1], \"expected\": [0, true, 1], \"passed\": true}], \"passed\": true}\n"}},"verified":true,"visibility":"public"}