add_action( 'rank_math/vars/register_extra_replacements', function() {
	rank_math_register_var_replacement(
		'woo_full_desc',
		[
			'name'        => esc_html__( 'Woo Full Desc.', 'rank-math' ),
			'description' => esc_html__( 'Woo Full Description...', 'rank-math' ),
			'variable'    => 'woo_full_desc',
			'example'     => woo_full_desc_callback(),
		],
		'woo_full_desc_callback'
	);
} );
function woo_full_desc_callback() {
	global $post;
	if ( empty( $post ) ) {
		return 'Product Description';
	}
	return substr(wp_strip_all_tags($post->post_content), 0, 160);
}