The calendar must be embedded within <form></form> tags. The form name must be
specified in the builder.
It is not necessary to specify the day, month and year field names if you
have only one calendar on the page. But we strongly recommend you to do so in
order to have control over the names of the input fields. By default, the
names are yr_num, mo_num and dt_num respectively.
If you have several calendars on the same page, the calendar name must be
different for each calendar.
If you have several calendars in the same form, the name of the year,
month and day field must be different for each calendar.