The day of the week, e.g. used to specify to which day the opening hours of an OpeningHoursSpecification refer.
Commonly used values:
http://purl.org/goodrelations/v1#Monday
http://purl.org/goodrelations/v1#Tuesday
http://purl.org/goodrelations/v1#Wednesday
http://purl.org/goodrelations/v1#Thursday
http://purl.org/goodrelations/v1#Friday
http://purl.org/goodrelations/v1#Saturday
http://purl.org/goodrelations/v1#Sunday
http://purl.org/goodrelations/v1#PublicHolidays