A text value that represents a Boolean value is required if this element is included. A value of true indicates that the item represents an all-day event. A value of false indicates that the item spans less than a user's working hours.
An all-day event spans the duration of working hours that is defined for a mailbox.
The schema that describes this element is located in the EWS virtual directory of the computer that is running MicrosoftExchange Server 2007 that has the Client Access server role installed.