nsIAccessibleSelectable Interface

 Return an nsIArray of selected nsIAccessible children 

nsIArray GetSelectedChildren()

 Adds the specified accessible child of the object to the
 object's selection.
 If the specified object is already selected, then it does nothing.
 @throws NS_ERROR_FAILURE if the specified object is not selectable.

void addChildToSelection(in long index)

 Clears the selection in the object so that no children in the object
 are selected.

void clearSelection()

 Determines if the current child of this object is selected
 @param The zero-based accessible child index
 @return Returns true if the child is selected, false if not.

boolean isChildSelected(in long index)

 Returns a reference to the accessible object representing the specified
 selected child of the object.
 @param index Zero-based selected accessible child index 
 @return The nth selected accessible child

nsIAccessible refSelection(in long index)

 Removes the specified child of the object from the object's selection.
 If the specified object was not selected, then it does nothing.
 @throws NS_ERROR_FAILURE if the specified object is not selectable.

void removeChildFromSelection(in long index)

 Select all children
 @return If the object does not accept multiple selection, return false.
         Otherwise, returns true.

boolean selectAllSelection()