Is it worth putting in the a property what warns on get/set? On one hand, most likely no one is using this, on the other hand it is not much work to make sure we do not needlessly break anyone who is trying to access this.

Originally posted by @tacaswell in #19348 (comment)

In #19348 the YearLocator.replaced attribute was not documented, nor was it tested, so it was dropped with an API note. @tacaswell suggested than maybe instead we should have a setter/getter that does the right thing?