code: @Nonnull
    public CollectingJSCodeProvider addAt (@Nonnegative final int nIndex, @Nullable final IHasJSCode aProvider)
    {
      if (aProvider != null)
        m_aList.add (nIndex, aProvider);
      return this;
    }
docs: Add JS code at the specified index.
  
  @param nIndex
  The index where the element should be added. Should be &ge; 0.
  @param aProvider
  The JS code provider to be added. May be <code>null</code>.
  @return this for chaining