code: public final ReadOnlyObjectProperty<Position> positionProperty() {
          if (position == null) {
              position = new ReadOnlyObjectWrapper<>(this, "position", _position); //$NON-NLS-1$
          }
          return position.getReadOnlyProperty();
      }
docs: A calendar entry can span multiple days. The position can be used if the
  view is shown on the "first" day, the "last" day, or some day in the
  "middle" of the span. If the entry is located on only one day then the
  position will be "only". This property is read-only and will be set by
  the framework.
  <p/>
  The image below illustrates this concept:
  <p/>
  <center><img src="doc-files/multi-days.png"></center>
  <p/>
  
  @return the position of the view within the time range of the calendar
  entry