code: protected FactoryBuilderSupport getProxyBuilder() {
          FactoryBuilderSupport proxy = localProxyBuilder.get();
          if (proxy == null) {
              return globalProxyBuilder;
          } else {
              return proxy;
          }
      }
docs: Proxy builders are useful for changing the building context, thus
  enabling mix &amp; match builders.
  
  @return the current builder that serves as a proxy.<br>