HTTP Content Negotiation and Quality Values

Many Internet resources have only one representation, meaning a single way in which they are stored or made available. In this situation, a client request to a server is an all-or-nothing proposition. The client may specify conditions under which it would like the server to send the resource, using the If- series of request headers described in the previous chapter. If the condition is met, the resource will be sent in the server's response in the one form in which it exists; if the condition is not met, no entity will be returned.

Other resources, however, may have multiple representations. The most common example is a document that is available in multiple languages, or one that is stored using more ...

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