This is a spin-off from #665, which conflates this issue's nominal topic with a discussion of the timeZone options. The text below is an extract of the original by @aphillips.

@eemeli noted that some literal values don't make sense with some of the date/time functions. Notably date literal with :time or time literal with :date.

In LDML45, I propose:

• :datetime accepts XMLSchema date, time, and dateTime types as literal operands.
• :date accepts date and dateTime
• :time accepts time and dateTime

Note that not accepting all three types on all three functions makes for potential issues with declarations, since the temporal value would be rejected instead of passed to later calls. Examples:

.local $date = {|2024-02-17| :datetime} // don't blow up! {{Today is {$date}.}}