Tag 4 indicates a decimal fraction represented by a tagged array with two items, an integer exponent and an integer or bignum mantissa. The value of a decimal fraction is m*(10**e).

Tag 3 is for negative bignums. These are encoded the same as for positive bignums (tag 2), but the value of the bignum is -1 - n.

Map of tag codes to read handlers to parse number values.

Map of number types to write handler functions.

Tag 2 is for positive bignums, which are encoded as a byte string data item. This is interpreted as an unsigned integer n in network byte order.

Tag 30 is used to represent a rational number composed of two integers, a numerator and a denominator.

See: http://peteroupc.github.io/CBOR/rational.html