code: protected boolean startProcessDocs(final RootDoc rootDoc) throws IOException {
          for (String[] options : rootDoc.options()) {
              parseOption(options);
          }
  
          // Make sure the user specified a settings directory OR that we should use the defaults.
          // Both are not allowed.
          // Neither are not allowed.
          if ( (useDefaultTemplates && isSettingsDirSet) ||
                  (!useDefaultTemplates && !isSettingsDirSet)) {
              throw new RuntimeException("ERROR: must specify only ONE of: " + USE_DEFAULT_TEMPLATES_OPTION + " , " + SETTINGS_DIR_OPTION);
          }
  
          // Make sure we can use the directory for settings we have set:
          if (!useDefaultTemplates) {
              validateSettingsDir();
          }
  
          // Make sure we're in a good state to run:
          validateDocletStartingState();
  
  
  
          processDocs(rootDoc);
          return true;
      }
docs: Extracts the contents of certain types of javadoc and adds them to an output file.
  
  @param rootDoc The documentation root.
  @return Whether the JavaDoc run succeeded.
  @throws java.io.IOException if output can't be written.