http://www.rfc-editor.org/rfc/rfc5987.txt
RFC 5987: Character Set and Language Encoding for Hypertext Transfer Protocol (HTTP) Header Field Parameters, J. Reschke2010-08-01T23:00:00-00:00By default, message header field parameters in Hypertext Transfer Protocol (HTTP) messages cannot carry characters outside the ISO- 8859-1 character set. RFC 2231 defines an encoding mechanism for use in Multipurpose Internet Mail Extensions (MIME) headers. This document specifies an encoding suitable for use in HTTP header fields that is compatible with a profile of the encoding defined in RFC 2231. [STANDARDS-TRACK]