WordPress at a glance
filter is not described

wp_unique_post_slug_is_bad_flat_slug filter-hook . WP 3.1.0

Filters whether the post slug would be bad as a flat slug.

Usage

add_filter( 'wp_unique_post_slug_is_bad_flat_slug', 'filter_function_name_5591', 10, 3 );
function filter_function_name_5591( $bad_slug, $slug, $post_type ){
	// filter...

	return $bad_slug;
}
$bad_slug(true/false)
Whether the post slug would be bad as a flat slug.
$slug(string)
The post slug.
$post_type(string)
Post type.

Where the hook is called

wp_unique_post_slug()
wp_unique_post_slug_is_bad_flat_slug
wp-includes/post.php 4009
if ( $post_name_check || in_array( $slug, $feeds ) || 'embed' === $slug || $conflicts_with_date_archive || apply_filters( 'wp_unique_post_slug_is_bad_flat_slug', false, $slug, $post_type ) ) {

Where the hook is used (in WP core)

Does not used.