<datebox id="db1" width="150px" constraint="before 20130420, no empty" />
<datebox id="db0" width="150px" constraint="no empty, before 20130420" />
The calendar of the former datebox does disable the dates after 20130420 to preventing against being selected,
whereas the latter does not disable the dates which the "before 20130420" is not at the first place of constraint=""