Index: src/core.js
===================================================================
--- src/core.js	(revision 5084)
+++ src/core.js	(working copy)
@@ -174,7 +174,7 @@
 		// Look for the case where we're accessing a style value
 		if ( name.constructor == String )
 			if ( value == undefined )
-				return this.length && jQuery[ type || "attr" ]( this[0], name ) || undefined;
+				return this[0] && jQuery[ type || "attr" ]( this[0], name );
 
 			else {
 				options = {};
@@ -1042,11 +1042,13 @@
 	attr: function( elem, name, value ) {
 		// don't set attributes on text and comment nodes
 		if (!elem || elem.nodeType == 3 || elem.nodeType == 8)
-			return undefined;
+			return;
 
 		var fix = jQuery.isXMLDoc( elem ) ?
 			{} :
-			jQuery.props;
+			jQuery.props,
+			get = value != undefined,//whether we are getting (or setting)
+			special = /href|src/.test( name );//these attributes need special treatment
 
 		// Safari mis-reports the default selected property of a hidden option
 		// Accessing the parent's selectedIndex property fixes it
@@ -1054,22 +1056,22 @@
 			elem.parentNode.selectedIndex;
 		
 		// Certain attributes only work when accessed via the old DOM 0 way
-		if ( fix[ name ] ) {
-			if ( value != undefined )
-				elem[ fix[ name ] ] = value;
+		if ( !special && ( fix[ name ] || name in elem ) ) {
+			if ( get )
+				elem[ fix[ name ] || name ] = value;
 
-			return elem[ fix[ name ] ];
+			return elem[ fix[ name ] || name ];
 
 		} else if ( jQuery.browser.msie && name == "style" )
 			return jQuery.attr( elem.style, "cssText", value );
 
-		else if ( value == undefined && jQuery.browser.msie && jQuery.nodeName( elem, "form" ) && (name == "action" || name == "method") )
+		else if ( get && jQuery.browser.msie && jQuery.nodeName( elem, "form" ) && (name == "action" || name == "method") )
 			return elem.getAttributeNode( name ).nodeValue;
 
 		// IE elem.getAttribute passes even for style
 		else if ( elem.tagName ) {
 
-			if ( value != undefined ) {
+			if ( get ) {
 				// We can't allow the type property to be changed (since it causes problems in IE)
 				if ( name == "type" && jQuery.nodeName( elem, "input" ) && elem.parentNode )
 					throw "type property can't be changed";
@@ -1078,7 +1080,7 @@
 				elem.setAttribute( name, "" + value );
 			}
 
-			if ( jQuery.browser.msie && /href|src/.test( name ) && !jQuery.isXMLDoc( elem ) ) 
+			if ( jQuery.browser.msie && special && !jQuery.isXMLDoc( elem ) ) 
 				return elem.getAttribute( name, 2 );
 
 			return elem.getAttribute( name );
@@ -1087,7 +1089,7 @@
 		} else {
 			// IE actually uses filters for opacity
 			if ( name == "opacity" && jQuery.browser.msie ) {
-				if ( value != undefined ) {
+				if ( get ) {
 					// IE has trouble with opacity if it does not have layout
 					// Force it by setting the zoom level
 					elem.zoom = 1; 
@@ -1106,7 +1108,7 @@
 				return letter.toUpperCase();
 			});
 
-			if ( value != undefined )
+			if ( get )
 				elem[ name ] = value;
 
 			return elem[ name ];
@@ -1234,18 +1236,8 @@
 		"float": styleFloat,
 		cssFloat: styleFloat,
 		styleFloat: styleFloat,
-		innerHTML: "innerHTML",
-		className: "className",
-		value: "value",
-		disabled: "disabled",
-		checked: "checked",
 		readonly: "readOnly",
-		selected: "selected",
-		maxlength: "maxLength",
-		selectedIndex: "selectedIndex",
-		defaultValue: "defaultValue",
-		tagName: "tagName",
-		nodeName: "nodeName"
+		maxlength: "maxLength"
 	}
 });