FA-53447 / Accessibility interaction semantics / Member archive

Reversed accessible ranges are collapsed · case 02

Reversed accessible ranges are collapsed.

Member previewVariant 2 · 3 implementations · 10 checks per implementation

Case contract

Input [text,start,end,unit] where indices are measured in utf16 or codepoint units. Negative indices count backward from end, clamp to valid extent, and sort reversed endpoints. A boundary inside a surrogate pair expands outward (start down, end up). CRLF is exposed as one LF after slicing. NUL becomes replacement character. Return [exposed_text,normalized_start,normalized_end,source_units]. UTF16 offsets refer to original source, not normalized text.

Why this case matters

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

One recorded failure

Sample boundary fixture

This sample comes from the broken implementation of a controlled reproducer.

Boundary fixture	Actual	Expected	Outcome
reverse	`["", 4, 4, 5]`	`["BCD", 1, 4, 5]`	Failed

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