docs: function() {
              if (!Object.keys(this.book.config.get('pluginsConfig.uml', {})).length) {
                  var book = this;
                  var output = book.output;
                  var name = output.name.toString();
  
                  // NOTE: This fixed issue #2
                  // https://github.com/vowstar/gitbook-plugin-uml/issues/2
                  // Use SVG format by default in website when user not give
                  // any configuration to get better result.
                  if (name == 'website') {
                      this.book.config.set('pluginsConfig.uml', {
                          format: 'svg'
                      });
                  } else {
                      this.book.config.set('pluginsConfig.uml', {
                          format: 'png'
                      });
                  }
              }
              var startNailgun = this.book.config.get('pluginsConfig.uml.nailgun', false);
              if (startNailgun && !nailgunRunning) {
                  plantuml.useNailgun(function() {
                      nailgunRunning = true;
                  });
              }
  
              // Copy images to output folder every time
              var book = this;
              var output = book.output;
              var rootPath = output.root();
              if (fs.existsSync(ASSET_PATH)) {
                  fs.mkdirs(path.join(rootPath, ASSET_PATH));
                  fs.copySync(ASSET_PATH, path.join(rootPath, ASSET_PATH));
              }
          }