From 0bb26cc2445243fa8afd88c576fb7e1d1c39c96c Mon Sep 17 00:00:00 2001
From: Anne van Kesteren <annevk@annevk.nl>
Date: Tue, 30 Oct 2018 16:23:33 +0100
Subject: [PATCH] Limit Content-Type overrides to when charset isn't already
 UTF-8

This will help web compatibility and address all cases linked from https://github.com/whatwg/mimesniff/issues/84.

Tests: https://github.com/web-platform-tests/wpt/pull/13779.
---
 xhr.bs | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/xhr.bs b/xhr.bs
index 98fe73c..c315786 100644
--- a/xhr.bs
+++ b/xhr.bs
@@ -723,8 +723,10 @@ method must run these steps:
        <a lt="parse a MIME type from bytes">parsing</a> <var>originalAuthorContentType</var>.
 
        <li>
-        <p>If <var>contentTypeRecord</var> is not failure, and <var>contentTypeRecord</var>'s
-        <a for="MIME type">parameters</a>["<code>charset</code>"] <a for=map>exists</a>, then:
+        <p>If <var>contentTypeRecord</var> is not failure, <var>contentTypeRecord</var>'s
+        <a for="MIME type">parameters</a>["<code>charset</code>"] <a for=map>exists</a>, and
+        <a for="MIME type">parameters</a>["<code>charset</code>"] is not an
+        <a>ASCII case-insensitive</a> match for "<code>UTF-8</code>", then:
 
         <ol>
          <li><p><a for=map>Set</a> <var>contentTypeRecord</var>'s