Issue #3436136 by dineshkumarbollu, joachim: Improve documentation for OptionsRequestSubscriber

/**

 * Handles options requests.

 *

 * Therefore it sends an options response using all methods on all possible

 * routes.

 * Listens to KernelEvents::REQUEST and responds to OPTIONS requests by

 * providing an Allow header listing all the HTTP methods allowed for the

 * requested routes.

 */

class OptionsRequestSubscriber implements EventSubscriberInterface {