Decide on date/time formatting string syntax

[seancolsen]

Context

When displaying dates and times, the front end will recieve the following two pieces of info:

• a string representation of the value in canonical form.
• a "formatting string", containing information about how to display the value to the user.

The front end needs to take these two strings and combine them into a formatted value.

The front end has total control over setting the formatting string and reading it. The back end only validates that it's 255 characters or less (discussion).

To-do

We need to decide how our formatting strings will work.

Prior art

• LibreOffice
• Moment
• Luxon
• date-fns
• Intl.DateTimeFormat (browser-native API, more limited)

Considerations

• We'll likely want to use a 3rd-party library to perform the formatting. As such, the work of evaluating and choosing that library may, in fact, be the only thing we need to do to close this ticket.
• Once users have set their formatting strings, it will not be easy for us to make backwards-incompatible changes to the formatting algorithm. This means that it's important that we choose a library which is stable and likey to have long-term support.

[seancolsen]

@pavish I've assigned this to you since you're taking the date/time portion of the data types milestone. I'm fine with picking either Luxon or date-fns. Probably whatever we pick, we'll end up regretting it later for some reason! 😜 So maybe flip a coin? That's where my thinking is currently.