UInt2


 * A UInt2 value is an unsigned integer of 2 bits.
 * It can only be 0, 1, 2 and 3.
 * Units of UInt2 have a pre-defined cardinality of 4, which cannot be overridden.
 * There is no undefined value indicator for UInt2.
 * UInt2 is a Sub Byte Element.
 * The GeoDms can store 16 UInt2 values in 4 bytes.
 * UInt2 can be the Domain of an Attribute, which implies that that Attribute has four values.