I think you should describe the underlying model for Blob/File so other specifications can more easily hook into it. E.g. if I want to represent a File object with a name /x/ and type /y/ there's not a clear way to do that right now. This also leads to issues such as it not being clear what the value space is of various properties.
E.g. "A |blob| provides asynchronous access to a byte sequence. A blob has an associated |type| which is a MIME type." (Which could be a link to the variant of MIME type you use.) And then you build the API on top of this model. -- http://annevankesteren.nl/
