Selects all elements that are the nth-child of their parent, counting from the last element to the first.
Because jQuery's implementation of :nth- selectors is strictly derived from the CSS specification, the value of n is "1-indexed", meaning that the counting starts at 1. For other selector expressions such as :eq() or :even jQuery follows JavaScript's "0-indexed" counting. Given a single <ul> containing three <li>s, $( "li:nth-last-chil