This is documentation for Mathematica 5, which was
based on an earlier version of the Wolfram Language.

 A.2.5 Numbers Input forms for numbers. Numbers can be entered with the notation base^^digits in any base from 2 to 36. The base itself is given in decimal. For bases larger than 10, additional digits are chosen from the letters a-z or A-Z. Upper- and lower-case letters are equivalent for these purposes. Floating-point numbers can be specified by including . in the digits sequence. In scientific notation, mantissa can contain ` marks. The exponent n must always be an integer, specified in decimal. The precision or accuracy s can be any real number; it does not need to be an integer. In the form base^^number`s the precision s is given in decimal, but it gives the effective number of digits of precision in the specified base, not in base 10. An approximate number x is taken to be machine precision if the number of digits given in it is Ceiling[\$MachinePrecision] + 1 or less. If more digits are given, then x is taken to be an arbitrary-precision number. The accuracy of x is taken to be the number of digits that appear to the right of the decimal point, while its precision is taken to be Log[10, Abs[x]] + Accuracy[x]. A number entered in the form 0``s is taken to have precision Indeterminate and accuracy s.