WordPress at a glance
filter is not described

sanitize_key filter-hook . WP 3.0.0

Filters a sanitized key string.

Usage

add_filter( 'sanitize_key', 'filter_function_name_7342', 10, 2 );
function filter_function_name_7342( $key, $raw_key ){
	// filter...

	return $key;
}
$key(string)
Sanitized key.
$raw_key(string)
The key prior to sanitization.

Where the hook is called

sanitize_key()
wp-includes/formatting.php 1913
return apply_filters( 'sanitize_key', $key, $raw_key );

Where the hook is used (in WP core)

Does not used.