$("p").has("em"); // only items with em elements
$("p").filter(".myclass"); // only element with class "myclass"
$("p").filter(":even"); // even numbered items
$("p").filter( $("p.myclass") ); // elements which appear in both sets
$("p").filter(function(i) { return (i % 3 == 0) }); // every third item
$("p").not(".myclass"); // elements without class "myclass"
$("p").not(":even"); // odd numbered items