---recycler-----

	// https://developer.wordpress.org/reference/functions/get_the_post_thumbnail/

		function get_the_post_thumbnail( $post = null, $size = 'post-thumbnail', $attr = '' ) {
		$post = get_post( $post );
		if ( ! $post ) {
			return '';
		}
		$post_thumbnail_id = get_post_thumbnail_id( $post );    // same as:   get_metadata('post', $post_id, '_thumbnail_id', $single);  ----- > that returns-----> 	$res = apply_filters( "get_{$meta_type}_metadata", null, $object_id, $meta_key, $single );

		$size = apply_filters( 'post_thumbnail_size', $size, $post->ID );

		if ( $post_thumbnail_id ) {

			do_action( 'begin_fetch_post_thumbnail_html', $post->ID, $post_thumbnail_id, $size );
			if ( in_the_loop() )
				update_post_thumbnail_cache();
			$html = wp_get_attachment_image( $post_thumbnail_id, $size, $icon=false, $attr );
			do_action( 'end_fetch_post_thumbnail_html', $post->ID, $post_thumbnail_id, $size );

		} else {
			$html = '';
		}
		.....