Simplified explanation

Author: mdoutreluingne

reference/configuration/security.rst

@@ -357,11 +357,9 @@ form_only
 
 **type**: ``boolean`` **default**: ``false``
 
-By setting this option to ``true``, there will be a check the content type, which will prevent the
-:class:`Symfony\\Component\\Security\\Http\Authenticator\\FormLoginAuthenticator` from responding to requests
-that should be handled by :class:`Symfony\\Component\\Security\\Http\Authenticator\\JsonLoginAuthenticator` (i.e. the
-method :method:`FormLoginAuthenticator::supports <Symfony\\Component\\Security\\Http\Authenticator\\FormLoginAuthenticator::supports>`
-will return ``false`` if the content type is ``application/json`` and ``true`` for form data).
+By setting this option to ``true`, a content type check will be performed when the login form is submitted
+(i.e. the login form will be processed if it is the form data, so with a
+content type `application/x-www-form-urlencoded`.
 
 .. versionadded:: 5.4