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encyclo - 3:09 pm on Mar 10, 2006 (gmt 0)
[w3.org...]
For application/xhtml+xml support, Opera only handles it correctly since version 7.10 (Windows), 6.1 (Linux/Unix) and 6.02 (Mac). For most version 6.x versions the mime type is recognized but handled incorrectly (case-insensitive). 5.x had no support. See this chart: