Numeric text in any accepted form, as truncateNumberText takes it. Only
digits, decimal and an exponent marker are read.
The decimal separator text is written with.
false when the leading significant digit sits outside 1E-309 … 1E+307
(1E-310, 0.00001E-305, 1E+308); for a zero mantissa, when its scale — exponent less
fraction digits — is outside ±308 (0E-309, 0.0E-308 and 0E+309, but not 0E-308,
000E-308 or 0.0E+309). Text out of range is not a number: a formula literal will not
commit, VALUE is #VALUE! and typed entry stays text.
Whether numeric text is inside the range accepted as a number, judged from the text as written rather than the double it parses to.