Field type or semantics for "last day of month"?

Termination dates of often are like “end of moth” or “end of year”. Or more complicated: “to the 15th or last day of the month”.

Does Tryton support some ways to express this? Thus one could either validate that some date matches this condition? Or some ideas for some notation for expressing this?

I’m aware of (see Field TimeDelta define a period in month. But: Is there a “modern” or a reusable version of this?