EDIT

We may need an additional field verbatimDate which is e.g. for references the date when the reference was published according to what is written on front page.

A couple of questions exist:

• do we need this field for all TimePeriods or only for usage in Reference => decision: references only
• what format should it have? String, Date, DateTime, TimePeriod, PartialDate, ... => decision: String

If it does not become a field within TimePeriod it may become more difficult to parse and format such dates as you need to implement separate parsers and formatters for this special use case.
But we could use a subclass VerbatimTimePeriod which has an extra field.

If it becomes a String it is not possible to format differently according to the needs of the output (e.g. the new IPNI format [dt. Jan 2013; issued 28 Dec 2012] then is not possible to use in a special publication when at other places we only want to have something like "2013" 2012

Other places where TimePeriod is currently used are: Classification.timeperiod, InstitutionalMembership.period, Person.lifespan, EvenBase.timeperiod (including subclasses Amplification, DerivationEvent, DeterminationEvent, GatheringEvent, MaterialOrMethodEvent [Cloning, PreservationMethod], SingleRead), DescriptionElementBase.timeperiod, NamedArea.validPeriod,

See also #6627#note-10

Open issues:

• Parsing and Formatting (#7429)
• TaxEditor implementation (#7421)
• Vaadin implementation (#7425)