code: function setErrorMessage(inputGroup, message) {
          var errorNode = this.getErrorNode(inputGroup);
          if (errorNode === false) {
              // container for error message doesn't exists, create new
              errorNode = this.createErrorNode();
              this.toggleErrorClass(inputGroup);
              this.insertErrorNode(inputGroup, errorNode);
          }
          // set or update error message
          errorNode.textContent = message;
      }
docs: Creates and includes into DOM error node or updates error message
  
  @param {HTMLElement} inputGroup
  @param {String} message