FA-96759 / Phone number formatting / Member archive

Pattern-driven phone input mask: escaped X consumes a digit · case 04

"E\XT XXXX" shows a backslash and uses the first digit as the X.

Member previewVariant 4 · 3 implementations · 9 checks per implementation

Case contract

Input [digits, pattern]. Each X consumes the next digit; "\" makes the next pattern character a literal; other characters are literals. Literals are buffered and written only in front of the next digit, so a partial input never ends in a literal; when the whole pattern was consumed the trailing literals are written too. More digits than X slots returns None.

Why this case matters

Input masks drive what users see while typing; stray punctuation, lost literals or silently dropped digits produce numbers that differ from what was typed.

One recorded failure

Sample boundary fixture

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

Boundary fixture	Actual	Expected	Outcome
escaped letter X	`"E\\8T 550"`	`"EXT 8550"`	Failed

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