[pielud]

You make a request for several ranges of a file using the range header, something like:

Range: bytes=100-200, 600-800, 1500-

If the server supports ranges, it will respond with a 206 Partial Content status, and send a multipart/byteranges response body, which looks like this http://www.freesoft.org/CIE/RFC/2068/225.htm. Basically a delimited string containing all the ranges.

This is useful for some streaming audio/video formats and especially for large pdfs. IIRC, pdfs typically have header information at the end of the file, so it's useful for a pdf reader to get the end of the file first.