first 与 first-child css_selector jquery中的区别

$("ul li:frist") 与$("ul li:first-child")的区别
$("ul li:frist") Selects the first
 element of the first 

$("ul li:frist-child") Selects the first
 element of every 
 

测试使用:http://www.w3schools.com/jquery/tryit.asp?filename=tryjquery_sel_ullifirst