  
 Index: include/httpd.h
 ===================================================================
---- include/httpd.h	(revision 1698089)
+--- include/httpd.h	(revision 1698116)
 +++ include/httpd.h	(working copy)
 @@ -518,6 +518,7 @@
  #define HTTP_UNSUPPORTED_MEDIA_TYPE          415

+#define AP_PROTOCOL_HTTP1		"http/1.1"
+
+/**
+ * Negotiate a possible protocol switch on the connection. The negotiation
+ * may start without any request sent, in which case the request is NULL. Or
+ * it may be triggered by the request received, e.g. through the "Upgrade"
+ * header.
+ * 
+ * The identifiers for protocols are taken from the TLS extension type ALPN:
+ * https://www.iana.org/assignments/tls-extensiontype-values/tls-extensiontype-values.xml
+ *
+ * If no protocols are added to the proposals, the server will always fallback
+ * to "http/1.1" which is the default protocol for connections that Apache
+ * handles. If the protocol selected from the proposals is the protocol
+ * already in place, no "protocol_switch" will be invoked.
+ *
+ * All hooks are run, unless one returns an error. Proposals may contain
+ * duplicates. The order in which proposals are added is usually ignored.

 #endif
Index: modules/http/http_protocol.c
===================================================================
--- modules/http/http_protocol.c	(revision 1698116)
+++ modules/http/http_protocol.c	(working copy)
@@ -135,7 +135,7 @@
     NULL, /* 418 */
