WordPress at a glance
filter is not described

pre_untrash_post filter-hook . WP 4.9.0

Filters whether a post untrashing should take place.

Usage

add_filter( 'pre_untrash_post', 'filter_function_name_5131', 10, 2 );
function filter_function_name_5131( $untrash, $post ){
	// filter...

	return $untrash;
}
$untrash(true/false)
Whether to go forward with untrashing.
$post(WP_Post)
Post object.

Where the hook is called

wp_untrash_post()
pre_untrash_post
wp-includes/post.php 2868
$check = apply_filters( 'pre_untrash_post', null, $post );

Where the hook is used (in WP core)

Does not used.