code: public final void add(Featurable featurable)
      {
          featurable.getFeature(Identifiable.class).addListener(this);
          toAdd.add(featurable);
          willAdd = true;
      }
docs: Add a featurable to the list. Will be added at the beginning of {@link #update(double)} call.
  If this function is called during {@link #update(double)}, it will be delayed to next {@link #update(double)}
  call.
  <p>
  Automatically add {@link IdentifiableModel} if feature does not have {@link Identifiable} feature.
  </p>
  
  @param featurable The featurable to add.