From the document: ‘Appendix B. Implementation Report: The encoding defined in this document currently is used for two different HTTP header fields: “Content-Disposition”, defined in [RFC6266], and “Link”, defined in [RFC5988]. As the encoding is a profile/clarification of the one defined in [RFC2231] in 1997, many user agents already supported it for use in “Content-Disposition” when [RFC5987] got published.
Since the publication of [RFC5987], two more popular desktop user agents have added support for this encoding; see http://purl.org/
NET/http/content-disposition-tests#encoding-2231-char for details. At this time, only one major
desktop user agent (Safari) does not support it.
Note that the implementation in Internet Explorer 9 does not support the ISO-8859-1 encoding; this document revision acknowledges that UTF-8 is sufficient for expressing all code points, and removes the requirement to support ISO-8859-1.’
Yay for UTF-8!
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