Index: test/unit/selector.js
===================================================================
--- test/unit/selector.js	(revision 4032)
+++ test/unit/selector.js	(working copy)
@@ -8,7 +8,8 @@
 		if ( all[i].nodeType == 8 )
 			good = false;
 	ok( good, "Select all elements, no comment nodes" );
-	t( "Element Selector", "p", ["firstp","ap","sndp","en","sap","first"] );
+	// make sure is case insensitive as well
+	t( "Element Selector", "P", ["firstp","ap","sndp","en","sap","first"] );
 	t( "Element Selector", "body", ["body"] );
 	t( "Element Selector", "html", ["html"] );
 	t( "Parent Element", "div p", ["firstp","ap","sndp","en","sap","first"] );
Index: src/core.js
===================================================================
--- src/core.js	(revision 4032)
+++ src/core.js	(working copy)
@@ -586,8 +586,8 @@
 	
 	// check if an element is in a (or is an) XML document
 	isXMLDoc: function( elem ) {
-		return elem.documentElement && !elem.body ||
-			elem.tagName && elem.ownerDocument && !elem.ownerDocument.body;
+		return elem && elem.documentElement && !elem.body ||
+			elem && elem.tagName && elem.ownerDocument && !elem.ownerDocument.body;
 	},
 
 	// Evalulates a script in a global context
@@ -612,6 +612,8 @@
 	},
 
 	nodeName: function( elem, name ) {
+		if (jQuery.isXMLDoc(elem.ownerDocument))
+			return elem.nodeName == name;
 		return elem.nodeName && elem.nodeName.toUpperCase() == name.toUpperCase();
 	},