code: private int clientIndexToTabIndex(final int clientIndex) {
  		int childCount = getTotalTabs();
  		int serverIndex = clientIndex;
  
  		for (int i = 0; i <= serverIndex && i < childCount; i++) {
  			if (!isTabVisible(i)) {
  				serverIndex++;
  			}
  		}
  
  		return serverIndex;
  	}
docs: The client-side tab indices will differ from the WTabSet's indices when one or more tabs are invisible.
  
  @param clientIndex the client-side index
  @return the WTabSet index corresponding to the given client index