true if c is a decimal digit; otherwise, false.
This method determines whether a char is a radix-10 digit. This contrasts with char.IsNumber(char), which determines whether a Char is of any numeric Unicode category. Numbers include characters such as fractions, subscripts, superscripts, Roman numerals, currency numerators, encircled numbers, and script-specific digits.
Valid digits are members of the System.Globalization.UnicodeCategory.DecimalDigitNumber category.