Make XML syntax definition mark invalid double-hyphen inside comment
diff --git a/a b/XML.tmLanguage
index 9438f60..bbb5823 100644
--- a/a
+++ b/XML.tmLanguage
@@ -109,6 +109,15 @@
<string>--%?></string>
<key>name</key>
<string>comment.block.xml</string>
+ <key>patterns</key>
+ <array>
+ <dict>
+ <key>match</key>
+ <string>--</string>
+ <key>name</key>
+ <string>invalid.illegal.double-hyphen-in-comment.xml</string>
+ </dict>
+ </array>
</dict>
<dict>
<key>begin</key>
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