[Commentor] LC-304 Ian Jacobs [Comment] * I am not sure what you mean by this checkpoint. Through Internet protocols I believe two parties can agree on whether a client supports a particular format available on the server. So do you mean that after such a negotiation, in (adapted) content you serve, you don't have to provide information about the format? I don't think you mean that, in particular because I think that would imply lots of communication about all the links in a document to determine the format of identified resources. * Other than through Internet protocols dynamically, I don't know how you can "know the device supports" a given format unless you are designing in a very closed environment, and I thought that the purpose of these guidelines was to explain how to design effectively in anopenenvironment. * Perhaps you can shorten this, therefore, to something like "To help users reduce the cost of unnecessary downloads, for pieces of content in formats that are not part of the default delivery context, identify the format in links." [Commentor reply] yes [Working Group decision] 
Most content adaptation systems rely on a database of known devices, with information on which format the device support. If you use such a system, you can annotated only the links you know may not be supported; if you don't, you fallback on the default delivery context, which tells you that only XHTML, JPG and GIF are supported formats (we have amended the text to clarify this).