Jquery selectors

$('#selected-plays > li').addClass('horizontal');

means find each list item (li) that is a child (>) of an element with an ID of

selected-plays (#selected-plays).

$('#selected-plays li:not(.horizontal)').addClass('sub-level');

we are getting every list item (li) that:

1. Is a descendant of an element with an ID of selected-plays

(#selected-plays), and

2. Does not have a class of horizontal (:not(.horizontal)).

jquery also use XPath selectors,like

$('a[@title]') means select all links that has a title attribut

$()'div[ol]') means get all div elements that contain an ol element

$('a[@href^="mailto:"]') means get all anchor elements(a) with an href attributes([@href]) that begin with mailto(^="mailto:")

$('a[@href$=".pdf"]') means get all links with a href attribute that ends with .pdf

$('a[@href*="mysite.com"]') means get all internal linkes,

Jquery's custom selectors

$('div.horizontal:eq(1)') means select the second item from a matched set of divs with a class of horizontal

$('tr:odd')

$('tr:even')

$('td:contains("henry")')