Allow ISO-conforming partial dates in properties

Use case or problem

Properties don’t allow partial dates like YYYY, YYYY-MM, and --MM-DD (even though these are ISO 8601 conforming).

Currently, when updating to the new properties view, old dates are filled with default data (20242024-01-01). And when trying to add a new property, incomplete dates aren’t saved (2024YYYY-MM-DD).

Two example issues:

  1. I want to track friends’ birthdays, but I don’t know/care about their birth year.
  2. I recall that I read a book in April 2023, but not the exact date (and that exact date isn’t important to me).

Proposed solution

When validating the “date” type in front-matter, allow year (YYYY), year-and-month (YYYY-MM), and month-and-day (--MM-DD).

Current workaround (optional)

Making up incorrect filler data.
Using old front-matter view (without validation).