Actualización

app/Resources/public/assets/modernizr/feature-detects/css-backgroundposition-shorthand.js

@@ -0,0 +1,19 @@
+/*
+    https://developer.mozilla.org/en/CSS/background-position
+    http://www.w3.org/TR/css3-background/#background-position
+
+    Example: http://jsfiddle.net/Blink/bBXvt/
+*/
+
+(function() {
+
+    var elem = document.createElement('a'),
+        eStyle = elem.style,
+        val = "right 10px bottom 10px";
+
+    Modernizr.addTest('bgpositionshorthand', function(){
+        eStyle.cssText = "background-position: " + val + ";";
+        return (eStyle.backgroundPosition === val);
+    });
+
+}());