The client may not be able to handle a very long document anyway. Short UDIs UDIs should be kept short and devoid of information that indicates the mechanism by which the document is retrieved. UDIs should only specify the contents. The document itself decides what it is and how to produce its contents. Normal documents contain their own text.
Indexes contain a cover page.
Indirect documents contain the mechanism for finding the real thing. See data model Ignore silently Any information a client or server does not understand it should ignore without complaints. The motivation is forward compatibility. Commands sent by new browsers to old servers should be ignored by those servers. In any case, from the next version, client and server always send the version number of the HTTP protocol they use, so the more recent of the two can choose to downgrade to the older version.