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docs/extensions/concept/index.md

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+# iCal4j Extensions - Concepts
+
+A concept is type definition for iCalendar components used to refine object data for specific scenarios.
+
+iCal4j Extensions includes concepts for common use-cases, as outlined in the table below.
+
+| Concept | Component | Scheduled | Planned | Participants (Active) | Repeats |
+|---------|-----------|-----------|---------|-----------------------|---------|
+| Event   | VEVENT | Yes | Yes | Yes | Optional |
+| Observance | VEVENT | Yes | Yes | No | Optional |
+| Action  | VTODO | No | Yes | Yes | Optional |
+| Issue | VTODO | No | No | Yes | No |
+| Request | VTODO | No | No | Yes | No |
+| Note | VJOURNAL | No | No | No | No |
+| Report | VJOURNAL | Yes | Yes | No | Optional |
+| Availability | VAVAILABILITY | Yes | Yes | No | Optional |
+
+* Scheduled - occurs on a specific date/time
+* Planned - represents a future activity or target (where not scheduled will typically have a due date)
+* Participants (Active) - requires actors to participate in order to resolve
+* Repeats - represents multiple related activities or targets