rfc2616 (HTTP/1.1):
A response to a request for a single range MUST NOT be sent using the multipart/byteranges media type.
A response to a request for multiple ranges, whose result is a single range, MAY be sent as a multipart/byteranges media type with one part.
A client that cannot decode a multipart/byteranges message MUST NOT ask for multiple byte-ranges in a single request.
If I understand this correctly, multiple ranges in a single request MAY use multipart/byteranges and clients MUST be able to decode it or shouldn't request it at all.
Does the "MAY" imply that there are also alternatives to multipart/byteranges that could be used? Do any exist? If so, are there headers to request them?
For example, could a server potentially concatenate all byte ranges into a single part response?
If a request asks for multiple ranges and the server can concatenate the requested ranges into a single continuous range, then the response can either:
use multipart/byteranges with a single MIME part for the concatenated range, where the part has its own Content-Range header.
send the concatenated data by itself and include a top-level Content-Range header.