how jQuery use sizzle selector

The call stack is as follow

return new jQuery.fn.init( selector, context ); 
 return (context || rootjQuery).find( selector ); 
 jQuery.find( selector, this[i], ret ); 
return makeArray(context.querySelectorAll(query), extra ); 

//if browser does not support W3C Selectors API
//will call this
//var Sizzle = function(selector, context, results, seed) { 



//jQuery.find = Sizzle