Specifies the days of the week that a ToD entry is potentially active. Used when relative (day- based) timing is required. A zero length string indicates that absolute (date-based) timing is required (i.e., TodStartDate and TodEndDate objects are not zero length). Week-day data is specified using a comma-separated list of week-day full names (e.g., 'monday,friday') or abbreviations (e.g., 'su,m,tu,w,th,f,sa' or 'sun,mon,tue,wed,thu,fri,sat'). Relative (day-based) and absolute (date-based) timing specification data are mutually exclusive.