code: private static Collection<ActionRef> getActionsInCommon(List<Selectable> selection)
      {
          final Collection<ActionRef> actions = new HashSet<>();
          final int n = selection.size();
          for (int i = 0; i < n; i++)
          {
              final Selectable selectable = selection.get(i);
              if (selectable.hasFeature(Actioner.class))
              {
                  final Actioner actioner = selectable.getFeature(Actioner.class);
                  checkActionsInCommon(actioner, actions);
              }
          }
          return actions;
      }
docs: Get all actions in common.
  
  @param selection The current selection.
  @return The actions in common.