code: function cleanUpAndMoveOn(evt) {
      var el = evt.target;
  
      // remove `error` CSS class, which may have been added by `FilterLeaf.prototype.invalid`
      el.classList.remove('filter-tree-error');
  
      // set or remove 'warning' CSS class, as per el.value
      FilterNode.setWarningClass(el);
  
      if (el === this.view.column) {
          // rebuild operator list according to selected column name or type, restoring selected item
          makeOpMenu.call(this, el.value);
      }
  
      if (el.value) {
          // find next sibling control, if any
          if (!el.multiple) {
              while ((el = el.nextElementSibling) && (!('name' in el) || el.value.trim() !== '')); // eslint-disable-line curly
          }
  
          // and click in it (opens select list)
          if (el && el.value.trim() === '') {
              el.value = ''; // rid of any white space
              FilterNode.clickIn(el);
          }
      }
  
      // forward the event to the application's event handler
      if (this.eventHandler) {
          this.eventHandler(evt);
      }
  }
docs: `change` event handler for all form controls.
  Rebuilds the operator drop-down as needed.
  Removes error CSS class from control.
  Adds warning CSS class from control if blank; removes if not blank.
  Adds warning CSS class from control if blank; removes if not blank.
  Moves focus to next non-blank sibling control.
  @this {FilterLeaf}