In BufferParams, we have both an isExportable method and an isExportableFormat method. Is there actually any functional difference between these? The latter may be slightly different, in that it passes the only_viewable flag to exportableFormats. But that could be handled quite differently, by just returning false if the format isn't viewable.
Richard PS "git blame" will show these as mine, but I just moved them to BufferParams from Buffer.
