code: function hideToolbarFadeOnFullScroll() {
  		editor
  			.$( [
  				editor.$( '.mce-inline-toolbar-grp .mce-container-body', document.body ),
  				editor.$( '.mce-toolbar-grp', editor.theme.panel.getEl() ),
  			] )
  			.each( ( i, toolbar ) => {
  				toolbar.on(
  					'scroll',
  					throttle( ( { target } ) => {
  						let action;
  						if ( target.scrollLeft === target.scrollWidth - target.clientWidth ) {
  							action = 'add';
  						} else if ( tinymce.DOM.hasClass( target, 'is-scrolled-full' ) ) {
  							action = 'remove';
  						}
  
  						if ( action ) {
  							const elements = editor.$( target );
  							if ( ! elements.hasClass( 'mce-container-body' ) ) {
  								elements.add( tinymce.DOM.getParent( target, '.mce-container-body' ) );
  							}
  
  							elements[ action + 'Class' ]( 'is-scrolled-full' );
  						}
  					}, 200 )
  				);
  			} );
  	}
docs: Monitors the toolbar's `scroll` event, applying a `.is-scrolled-full`
  class if and only if the left scroll position has reached the element's
  maximum scroll offset.