之所以把这部分放在这里，是因为这里用到了一些基本API，前一篇介绍过后才能使用。

//jQuery通过find方法调用Sizzle引擎
//jQuery通过find方法调用Sizzle引擎
jQuery.find = Sizzle;
jQuery.expr = Sizzle.selectors;
jQuery.expr[":"] = jQuery.expr.pseudos;
jQuery.unique = Sizzle.uniqueSort;
jQuery.text = Sizzle.getText;
jQuery.isXMLDoc = Sizzle.isXML;
jQuery.contains = Sizzle.contains;var rneedsContext = jQuery.expr.match.needsContext;//匹配没有其他如class等任何属性的标签，就是简单标签，
//如<input />和<div></div>
var rsingleTag = (/^<(\w+)\s*\/?>(?:<\/\1>|)$/);//当selector为 .header这样的形式则为简单选择符
var risSimple = /^.[^:#\[\.,]*$/;// Implement the identical functionality for filter and not
//比较难啃的一个函数，传入参数有几种用法。后面的多个过滤函数都依赖于这个函数
//第一个参数表示element元素集，第二个参数传入过滤函数、DOM、选择符、数组，第三个参数为预设结果
function winnow( elements, qualifier, not ) {if ( jQuery.isFunction( qualifier ) ) {return jQuery.grep( elements, function( elem, i ) {/* jshint -W018 */return !!qualifier.call( elem, i, elem ) !== not;});}if ( qualifier.nodeType ) {return jQuery.grep( elements, function( elem ) {return ( elem === qualifier ) !== not;});}if ( typeof qualifier === "string" ) {if ( risSimple.test( qualifier ) ) {return jQuery.filter( qualifier, elements, not );}qualifier = jQuery.filter( qualifier, elements );}return jQuery.grep( elements, function( elem ) {return ( jQuery.inArray( elem, qualifier ) >= 0 ) !== not;});
}//过滤函数
jQuery.filter = function( expr, elems, not ) {var elem = elems[ 0 ];if ( not ) {expr = ":not(" + expr + ")";}//其实这两个区别不大，都要调用Sizzlereturn elems.length === 1 && elem.nodeType === 1 ?jQuery.find.matchesSelector( elem, expr ) ? [ elem ] : [] :jQuery.find.matches( expr, jQuery.grep( elems, function( elem ) {return elem.nodeType === 1;}));
};//开始jQuery对象的原型进行扩展
jQuery.fn.extend({find: function( selector ) {var i,ret = [],self = this,len = self.length;//当传入的参数是字符串类型时，调用下面的filter方法，本质是调用上面的winnow，winnow里又视情况调用sizzleif ( typeof selector !== "string" ) {return this.pushStack( jQuery( selector ).filter(function() {console.log('find');console.log(self);for ( i = 0; i < len; i++ ) {//如果self包含符合selector的this，注意这里的this是新的jQuery对象if ( jQuery.contains( self[ i ], this ) ) {return true;}}}) );}//否则以self[i]为查找上下文context进行查找for ( i = 0; i < len; i++ ) {jQuery.find( selector, self[ i ], ret );}// Needed because $( selector, context ) becomes $( context ).find( selector )//这里是正常的压栈和选择符拼接ret = this.pushStack( len > 1 ? jQuery.unique( ret ) : ret );ret.selector = this.selector ? this.selector + " " + selector : selector;return ret;},filter: function( selector ) {return this.pushStack( winnow(this, selector || [], false) );},not: function( selector ) {return this.pushStack( winnow(this, selector || [], true) );},is: function( selector ) {//通过winnow返回的长度来判断return !!winnow(this,// If this is a positional/relative selector, check membership in the returned set// so $("p:first").is("p:last") won't return true for a doc with two "p".typeof selector === "string" && rneedsContext.test( selector ) ?jQuery( selector ) :selector || [],false).length;}
});