Numeric text in any accepted form — signed, grouped, percent,
currency-affixed, or scientific. The scan is locale-blind: only digit
characters count toward significance (separators pass through untouched),
leading zeros carry none, and the scan stops at an exponent marker so E5
keeps its magnitude. Excess digits are zeroed rather than dropped so the
text's shape (decimal places, grouping) survives for format inference.
Applies Excel's entry rule to numeric text: every significand digit past the 15th becomes
0, so the text parses to the double Excel would store.