code: protected SortedSources getSources() {
          SortedSources sources = new SortedSources(getUserSources());
          if (addDefaultSourcesFlag()) {
              sources.addAll(DefaultSources.getDefaultSources(getClassLoader()));
          }
          if (addDiscoveredSourcesFlag()) {
              sources.addAll(DefaultSources.getDiscoveredSources(getClassLoader()));
          }
          sources = sources.unmodifiable();
          return sources;
      }
docs: Get the sources, default, discovered and user registered sources are
  included as appropriate.
  
  Call this method only from within a 'synchronized(this) block
  
  @return sources as a sorted set