code: public void addLinkRef (@Nonnull final String sKey, final LinkRef aLinkRef)
    {
      m_aLinkRefs.put (sKey.toLowerCase (Locale.US), aLinkRef);
    }
docs: Adds a LinkRef to this set of LinkRefs.
  
  @param sKey
  The key/id.
  @param aLinkRef
  The LinkRef.