docs: function ensureCodeBehind(code_behind) {
      if (typeof code_behind === 'undefined')
          throw "Missing mandatory global variable CODE_BEHIND!";
  
      var i, funcName;
      for (i = 1; i < arguments.length; i++) {
          funcName = arguments[i];
          if (typeof code_behind[funcName] !== 'function')
              throw "Expected CODE_BEHIND." + funcName + " to be a function!";
      }
  }