code: public boolean removeAll(Collection<?> c) {
          if (!(c instanceof JumboEnumSet))
              return super.removeAll(c);
  
          JumboEnumSet<?> es = (JumboEnumSet<?>)c;
          if (es.elementType != elementType)
              return false;
  
          for (int i = 0; i < elements.length; i++)
              elements[i] &= ~es.elements[i];
          return recalculateSize();
      }
docs: Removes from this set all of its elements that are contained in
  the specified collection.
  
  @param c elements to be removed from this set
  @return <tt>true</tt> if this set changed as a result of the call
  @throws NullPointerException if the specified collection is null