current state

The current datebox calendar popup can be used to select a day.
If the user switches views, he will be able to display the yearly and monthly view.
Clicking on a year (in yearly view) will go to the monthly view for the selected year. Clicking on a month (on the monthly view) will go to the daily view for the selected month. Clicking on a day will select it.

Feature

Some use cases may require selecting a month, or a year (not a full date up to day). A feature for datebox might be useful to limit the date selection to year or month.
See the attached example for a test implementation.