+ * Retrieve the post thumbnail.
+ *
+ * When a theme adds 'post-thumbnail' support, a special 'post-thumbnail' image size
+ * is registered, which differs from the 'thumbnail' image size managed via the
+ * Settings > Media screen.
+ *
+ * When using the_post_thumbnail() or related functions, the 'post-thumbnail' image
+ * size is used by default, though a different size can be specified instead as needed.