docs: improve virtual list item accessible name generator docs (#8356)

Author: tomivirkki

packages/virtual-list/src/vaadin-virtual-list-mixin.d.ts

@@ -55,6 +55,10 @@ export declare class VirtualListMixinClass<TItem = VirtualListDefaultItem> {
 
   /**
    * A function that generates accessible names for virtual list items.
+   * The function gets the item as an argument and the
+   * return value should be a string representing that item. The
+   * result gets applied to the corresponding virtual list child element
+   * as an `aria-label` attribute.
    */
   itemAccessibleNameGenerator?: (item: TItem) => string;
 

packages/virtual-list/src/vaadin-virtual-list-mixin.js

@@ -38,6 +38,10 @@ export const VirtualListMixin = (superClass) =>
 
         /**
          * A function that generates accessible names for virtual list items.
+         * The function gets the item as an argument and the
+         * return value should be a string representing that item. The
+         * result gets applied to the corresponding virtual list child element
+         * as an `aria-label` attribute.
          */
         itemAccessibleNameGenerator: {
           type: Function,