selector jquery
$("*") // all elements
$("p.demo") // <p> elements with class="intro"
$("p:first") // the first <p> element
$("p span") // span, descendant of p
$("p > span") // span, direct child of p
$("p + span") // span immediately proceeded by a p
$("p ~ span") // strong element proceeded by p
$("ul li:first") // the first <li> element of the first <ul>
$("ul li:first-child") // the first <li> element of every <ul>
$("ul li:nth-child(3)") // third child
$("[href]") // any element with an href attribute
$("a[target='_blank']") // <a> elements with a target "_blank" attribute
$("a[target!='_blank']") // <a> elements with a target attribute value other than "_blank"
$(":input") // all form elements
$(":button") // <button> and <input> elements of type="button"
$("tr:even") // even <tr> elements
$("tr:odd") // odd <tr> elements
$("span:parent") // element which has child element
$("span:contains('demo')") // element conaining the specified text