opacity is now retrieved from stylesheet in IE. fixes #3981

src/css.js

@@ -120,12 +120,18 @@ jQuery.extend({
 	},
 
 	curCSS: function( elem, name, force ) {
-		var ret, style = elem.style;
+		var ret, style = elem.style, filter;
 
 		// IE uses filters for opacity
 		if ( !jQuery.support.opacity && name == "opacity" ) {
-			ret = style.filter && style.filter.indexOf("opacity=") >= 0 ?
-				(parseFloat( style.filter.match(/opacity=([^)]*)/)[1] ) / 100) + '':
+			filter = (filter = style.filter) && filter.indexOf("opacity=") >= 0 ?
+				filter :
+				(filter = elem.currentStyle[ 'filter' ]) && filter.indexOf("opacity=") >= 0 ?
+					filter :
+					null;
+
+			ret = filter && filter.indexOf("opacity=") >= 0 ?
+				(parseFloat( filter.match(/opacity=([^)]*)/)[1] ) / 100) + '':
 				"";
 
 			return ret === "" ?

test/index.html

@@ -4,6 +4,9 @@
 	<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
 	<title>jQuery Test Suite</title>
 	<link rel="Stylesheet" media="screen" href="qunit/testsuite.css" />
+	<style type="text/css" media="screen">
+		ol#empty { opacity: 0; filter:Alpha(opacity=0); } /* for testing opacity set in styles in IE */
+	</style>
 	<!-- Includes -->
 	<script type="text/javascript">
 		var jQuery = this.jQuery || "jQuery", // For testing .noConflict()

test/unit/css.js

 module("css");
 
 test("css(String|Hash)", function() {
-	expect(21);
+	expect(23);
 
 	equals( jQuery('#main').css("display"), 'none', 'Check for css property "display"');
 
@@ -34,6 +34,10 @@ test("css(String|Hash)", function() {
 	});
 	jQuery('#foo').css({opacity: ''});
 	equals( jQuery('#foo').css('opacity'), '1', "Assert opacity is 1 when set to an empty String" );
+
+	equals( jQuery('#empty').css('opacity'), '0', "Assert opacity is accessible via filter property set in stylesheet in IE" );
+	jQuery('#empty').css({ opacity: '1' });
+	equals( jQuery('#empty').css('opacity'), '1', "Assert opacity is taken from style attribute when set vs stylesheet in IE with filters" );
 });
 
 test("css(String, Object)", function() {