Registers an embed handler.
Do not use this function directly, use wp_embed_register_handler() instead.
This function should probably also only be used for sites that do not support oEmbed.
(string) (Required) An internal ID/name for the handler. Needs to be unique.
(string) (Required) The regex that will be used to see if this handler should be used for a URL.
(callable) (Required) The callback function that will be called if the regex is matched.
(int) (Optional) Used to specify the order in which the registered handlers will be tested (default: 10). Lower numbers correspond with earlier testing, and handlers with the same priority are tested in the order in which they were added to the action.
Default value: 10