+SetField is a subclass of BiGintegerField that represents a set of values
+implemented as binary set. When initializing the caller must pass choices
+keyword argument whose values must be powers of 2.
+SetField is display friendly. The default widget for it is CheckboxSelectMultipleForSetField.
+ from xdjango.db.models.fields import SetField
+ from django import models
+ name = models.TextField()
+ specialties = SetField(choices=((PIZZA,"pizza"),(PASTA,"pasta"),(SEAFOOD,"seafood")))
+ >>> joes = Restaurant()
+ >>> joes.name = "Joe's Finest"
+ >>> joes.specialties = PIZZA|PASTA
+ >>> joes.get_specialties_display()
+A special field for storing week days. At the db level it is stored as string
+representing ordered values of ISO weekdays, e.g., "01" means "Monday and Tuesday"
+and "" for empty weekday set.
+To limit weekday choices (e.g., if you need to make sure that only Monday
+to Friday are selectable), subclass WeekdaySetField and give it a custom
+ weekday_choices = my_weekday_choices