This specification modifies the definition of the "CATEGORIES" property to allow it to be defined in an iCalendar object. The following additions are made to the definition of this property, originally specified in Section 188.8.131.52 of [RFC5545].
This property defines the categories for an entire calendar.
This property can be specified multiple times in an iCalendar object.
When multiple properties are present, the set of categories that apply to the iCalendar object are the union of all the categories listed in each property value.