http byte range request

http://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html#sec14.35.2

http://en.wikipedia.org/wiki/List_of_HTTP_header_fields

http://www.web-polygraph.org/docs/userman/ranges.html

http://labs.apache.org/webarch/http/draft-fielding-http/p5-range.html

http://www.askapache.com/htaccess/apache-status-code-headers-errordocument.html