Determines whether the control element represented by this segment is the primary element of a multi-element selection.
HRESULT retVal = object.IsPrimary(pfPrimary);
Pointer to a BOOL that receives TRUE if the element is the primary element, or FALSE otherwise.
If this method succeeds, it returns S_OK. Otherwise, it returns an HRESULT error code.
The primary element of a multiple selection is typically the first one a user chose when making the selection. The primary element typically has distinctive handles that indicate it is the primary element (for example, it might have white handles while all the other selected elements have black ones).
You might, for example, use the primary element as the reference point for an aligning operation.