Value

Constants::CALLBACK_TYPE_STRING = 1

Semantics

Every action callback returns array( $callback_type, $payload ) from execute_callback(). With CALLBACK_TYPE_STRING:

The payload is a raw HTML string. The dispatcher wraps it in a <div> and sends it as a success response; the calling JS decides where to insert it.

Typical usage

Inline rendering of small fragments where no modal is wanted.

public function execute_callback(): array {
    return array( Constants::CALLBACK_TYPE_STRING, $payload );
}