FA-80359 / Bidirectional text layout / Member archive

First-strong paragraph direction: numbers as strong · case 04

Paragraphs that start with a number become left-to-right.

Member previewVariant 4 · 3 implementations · 8 checks per implementation

Case contract

Input [bidi classes, default level]. Scan for the first L (level 0) or R/AL (level 1), skipping characters between an isolate initiator (LRI, RLI, FSI) and its matching PDI (nesting counted; an unmatched PDI is ignored). Embedding codes are not skipped. Return [level, index of deciding character] or [default, None].

Why this case matters

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.

One recorded failure

Sample boundary fixture

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

Boundary fixture	Actual	Expected	Outcome
regression: numbers as strong	`[0, 0]`	`[1, 2]`	Failed

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