code: public SourceVersion getSupportedSourceVersion() {
          SupportedSourceVersion ssv = this.getClass().getAnnotation(SupportedSourceVersion.class);
          SourceVersion sv = null;
          if (ssv == null) {
              sv = SourceVersion.RELEASE_6;
              if (isInitialized())
                  processingEnv.getMessager().printMessage(Diagnostic.Kind.WARNING,
                                                           "No SupportedSourceVersion annotation " +
                                                           "found on " + this.getClass().getName() +
                                                           ", returning " + sv + ".");
          } else
              sv = ssv.value();
          return sv;
      }
docs: If the processor class is annotated with {@link
  SupportedSourceVersion}, return the source version in the
  annotation.  If the class is not so annotated, {@link
  SourceVersion#RELEASE_6} is returned.
  
  @return the latest source version supported by this processor