Primitive type 'real'
Fractional numbers. Typically used whenever quantities are measured, estimated, or computed from other real numbers. The typical representation is decimal, where the number of significant decimal digits is known as the precision. Real numbers are needed beyond integers whenever quantities of the real world are measured, estimated, or computed from other real numbers. The term "Real number" in this specification is used to mean that fractional values are covered without necessarily implying the full set of the mathematical real numbers.
A rational number with implicit precision
Do not use an IEEE type floating point type, instead use something that works like a true decimal, with inbuilt precision (e.g. Java BigInteger)
All FHIR elements must have a @value or children
hasValue() or (children().count() > id.count())
unique id for the element within a resource (for internal references)
Must have either extensions or value[x], not both