code: function selectLanguage(options, lang) {
      let langToUse = lang;
      if (langToUse === '' && options.defaultLanguageForUnspecified !== undefined) {
          langToUse = options.defaultLanguageForUnspecified;
      }
      let prismLang = loadPrismLang(langToUse);
      if (prismLang === undefined && options.defaultLanguageForUnknown !== undefined) {
          langToUse = options.defaultLanguageForUnknown;
          prismLang = loadPrismLang(langToUse);
      }
      return [langToUse, prismLang];
  }
docs: Select the language to use for highlighting, based on the provided options and the specified language.
  
  @param {Object} options
  The options that were used to initialise the plugin.
  @param {String} lang
  Code of the language to highlight the text in.
  @return {Array} An array where the first element is the name of the language to use, and the second element is the PRISM language object for that language.