code: function setTabIndexOnEditorIframe( tabindex ) {
  	return function() {
  		// At this point, there's an iframe in the DOM with the id of `${editor.id}_ifr`.
  		// Can't find a way to get at it without hopping out to the DOM :/
  		const editorIframe = document.getElementById( `${ this.id }_ifr` );
  
  		if ( ! editorIframe ) {
  			return;
  		}
  
  		editorIframe.setAttribute( 'tabIndex', tabindex );
  	};
  }
docs: Returns a function that sets the tabindex on an editor instance. The returned function assumes that `this` is set to the editor instance