WordPress Version: 6.2
/**
* Checks if a meta key is registered.
*
* @since 4.6.0
* @since 4.9.8 The `$object_subtype` parameter was added.
*
* @param string $object_type Type of object metadata is for. Accepts 'post', 'comment', 'term', 'user',
* or any other object type with an associated meta table.
* @param string $meta_key Metadata key.
* @param string $object_subtype Optional. The subtype of the object type. Default empty string.
* @return bool True if the meta key is registered to the object type and, if provided,
* the object subtype. False if not.
*/
function registered_meta_key_exists($object_type, $meta_key, $object_subtype = '')
{
$meta_keys = get_registered_meta_keys($object_type, $object_subtype);
return isset($meta_keys[$meta_key]);
}