BEGIN:VCALENDAR
BEGIN:VEVENT
UID:1
SUMMARY:Event with a category
DESCRIPTION:Details for an event with a category
CATEGORIES:cat1,cat2,cat3
END:VEVENT
BEGIN:VEVENT
UID:2
SUMMARY:Event with a category
DESCRIPTION:Details for an event with a category
CATEGORIES:cat1  ,  cat2,   cat3
END:VEVENT
BEGIN:VEVENT
UID:3
SUMMARY:Event with a category
DESCRIPTION:Details for an event with a category
CATEGORIES:
END:VEVENT
BEGIN:VEVENT
UID:4
SUMMARY:Event with a category
DESCRIPTION:Details for an event with a category
CATEGORIES:lonely-cat
END:VEVENT
BEGIN:VEVENT
UID:5
SUMMARY:Event with a category
DESCRIPTION:Details for an event with a category
CATEGORIES:cat1
CATEGORIES:cat2
CATEGORIES:cat3
END:VEVENT
END:VCALENDAR