A lot of times, people want to omit the "current" part of a datetime. E.g. show 4 Jan 2026 during 2025 or 2027, but just 4 Jan during 2026. Or 4 Jan 15:17 most of the time, but just 15:17 on 4 Jan itself.
This can, of course, be done with surrounding logic in JavaScript (assuming there aren't cultural aspects of which "current" parts are omitted...), but it can't in HTML or (I think) MessageFormat. If we're aligning JavaScript with those other systems, it might be worth aligning this part too.
A lot of times, people want to omit the "current" part of a datetime. E.g. show 4 Jan 2026 during 2025 or 2027, but just 4 Jan during 2026. Or 4 Jan 15:17 most of the time, but just 15:17 on 4 Jan itself.
This can, of course, be done with surrounding logic in JavaScript (assuming there aren't cultural aspects of which "current" parts are omitted...), but it can't in HTML or (I think) MessageFormat. If we're aligning JavaScript with those other systems, it might be worth aligning this part too.