もしかしたら補完かけてくれるUAが存在するのかもしらんが、べつにそれは必須じゃない。

% telnet www.example.com 80
Trying 192.0.34.166...
Connected to www.example.com.
Escape character is '^]'.
HEAD http://www.example.com HTTP/1.0

HTTP/1.1 200 OK
Date: Wed, 26 Nov 2003 03:37:39 GMT
Server: Apache/1.3.27 (Unix) (Red-Hat/Linux)
Last-Modified: Wed, 08 Jan 2003 23:11:55 GMT
ETag: "3f80f-1b6-3e1cb03b"
Accept-Ranges: bytes
Content-Length: 438
Connection: close
Content-Type: text/html

Connection closed by foreign host.