Sometimes is necessary to know the day number/name for such date. Sometimes just
what was the first day of such month or year.

The idea is:
{{dayofweek:2006|08|24}} returns 4 (Thursday)
{{dayofweek:2006|08}} returns 2 (Tuesday) (= Aug 1st)
{{dayofweek:2006}} returns 7 (Sunday) (= Jan 1st)
missing parameter has default value 1

Name it different if you'll find proposed name confusing.

Version: unspecified
Severity: enhancement