If one has time to read prior art, I'd suggest giving the Health Level
7 v3.0 Data Types Specification
http://amisha.pragmaticdata.com/v3dt/report.html a look.
Of course HL7 has a lot of things to worry about which are off topic
for us, starting with a prior completely different version of the
standard. And much emphasis goes to coded values (enums) and coding
systems, but it is a nice review of issues found and solved by many
eyeballs and years.
Peter