Update description

Mainpage.dox

@@ -8,8 +8,8 @@
  * @section desc Description
  *
  * This library provides access to KAlarm calendar data, but not to the storage
- * of the data, which is handled by Akonadi (or by build option, KResources).
- * The main class, KAEvent represents a KAlarm event, and contains both the
+ * of the data, which is handled separately.
+ * The main class, KAEvent, represents a KAlarm event, and contains both the
  * event definition including the main alarm and optional subsidiary alarms, and
  * status information about the event.
  *
@@ -18,8 +18,12 @@
  * iCalendar product ID.
  *
  * Recurrence and sub-repetition information is represented by the KARecurrence
- * and Repetition classes respectively. The DateTime class is similar to
- * KDateTime but with a configurable start-of-day time for date-only times.
+ * and Repetition classes respectively.
+ *
+ * The KADateTime class is analagous to QDateTime, but can alternatively hold
+ * a date-only value, and its time zone definition is more flexible than
+ * QDateTime. The DateTime class is similar to KADateTime but with a
+ * configurable start-of-day time for date-only times.
  *
  * Three Akonadi attributes, for Collections and Items, are provided by
  * CollectionAttribute, CompatibilityAttribute and EventAttribute classes.