Post Type rewrite rules

Nest a page under a post type archive:

 
function my_rewrite_rules_array( $rules ) {
	$rules = array_merge( array(
		'post-type/pagename/?$'   => 'index.php?pagename=post-type/pagename',
	), $rules );
 
	return $rules;
}
add_filter( 'rewrite_rules_array', 'my_rewrite_rules_array' );

Nest a second post type under a main post type:

 
function my_rewrite_rules( $rules ) {
        $newrules = array();
        $newrules['^.*/second-post-type-slug/([^/]+)$'] = 'index.php?your_post_type=$matches[1]&post_type=your_post_type';
        return $newrules + $rules;
}