Issue #11567 - Let's have the DOCTYPE as HTML instead of XHTML.
diff --git a/Lib/http/server.py b/Lib/http/server.py
index 0cd8d35..fccdc4c 100644
--- a/Lib/http/server.py
+++ b/Lib/http/server.py
@@ -103,11 +103,10 @@
# Default error message template
DEFAULT_ERROR_MESSAGE = """\
-<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN"
- "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
-<html xmlns="http://www.w3.org/1999/xhtml">
+<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN"
+ "http://www.w3.org/TR/html4/strict.dtd">
<head>
- <meta http-equiv="Content-Type" content="text/html;charset=utf-8" />
+ <meta http-equiv="Content-Type" content="text/html;charset=utf-8">
<title>Error response</title>
</head>
<body>