Accept either a day, a month or a year from the user
On my website, users can provide a source to a blog post. This source is dated. I'd like my users to provide either,
- a day (format is dd/mm/yyyy),
- a month (format is mm/yyyy),
- a year (format could be -y[yyyy] for BC years to y[yyy] for AD years).
and I'd like it to be in a single input.
How can I find an intuitive way to indicate the various format I accept to my users?