docs: function encodeBookToJson(book) {
      var config = book.getConfig();
      var language = book.getLanguage();
  
      var variables = config.getValue('variables', {});
  
      return {
          summary: encodeSummary(book.getSummary()),
          glossary: encodeGlossary(book.getGlossary()),
          readme: encodeReadme(book.getReadme()),
          config: book.getConfig().getValues().toJS(),
  
          languages: book.isMultilingual()? encodeLanguages(book.getLanguages()) : undefined,
  
          gitbook: {
              version: gitbook.version,
              time: gitbook.START_TIME
          },
          book: extend({
              language: language? language : undefined
          }, variables.toJS())
      };
  }