jquery后来人选择器不同写法的区别 _JavaScript

jquery后代选择器不同写法的区别？
jquery后代选择器有多种写法，如下都能达到目的，哪位高人知道他们之间的核心区别是什么?

$("#tab_schedule").find("li");

$("#tab_schedule li");

$("li","#tab_schedule");

------解决方案--------------------
主要是作用上有所区别
比如
当this 为 #tab_schedule 时怎么获取子元素li？
$(this).find('li');
这样就ok

$("li","#tab_schedule");
这个不是分组选择器吗？怎么是后代选择器了？

可能是楼主这个例子中
#tab_schedule 下正好有li
而分组取出来的dom，有li 有#tab_schedule，所以楼主就认为是后代选择器了。
------解决方案--------------------
$("#tab_schedule").find("li")、$("li","#tab_schedule")这俩个是完全等价的。
------解决方案--------------------
后代选择器的内部实现在文档中没有特别说明。我觉得这三种查找方法在内部实现都是一样的，都是先获取祖宗对象集合，再通过find()方法进行遍历查找，比如：
$("#tab_schedule ul li") 等价于 $("#tab_schedule").find("ul").find("li")
------解决方案--------------------

HTML code

jQuery.fn = jQuery.prototype = {
    constructor: jQuery,
    init: function( selector, context, rootjQuery ) {
        var match, elem, ret, doc;

        // Handle $(""), $(null), or $(undefined)
        if ( !selector ) {
            return this;
        }

        // Handle $(DOMElement)
        if ( selector.nodeType ) {
            this.context = this[0] = selector;
            this.length = 1;
            return this;
        }

        // The body element only exists once, optimize finding it
        if ( selector === "body" && !context && document.body ) {
            this.context = document;
            this[0] = document.body;
            this.selector = selector;
            this.length = 1;
            return this;
        }

        // Handle HTML strings
        if ( typeof selector === "string" ) {
            // Are we dealing with HTML string or an ID?
            if ( selector.charAt(0) === "<" && selector.charAt( selector.length - 1 ) === ">" && selector.length >= 3 ) {
                // Assume that strings that start and end with <> are HTML and skip the regex check
                match = [ null, selector, null ];

            } else {
                match = quickExpr.exec( selector );
            }

            // Verify a match, and that no context was specified for #id
            if ( match && (match[1] || !context) ) {

                // HANDLE: $(html) -> $(array)
                if ( match[1] ) {
                    context = context instanceof jQuery ? context[0] : context;
                    doc = ( context ? context.ownerDocument || context : document );

                    // If a single string is passed in and it's a single tag
                    // just do a createElement and skip the rest
                    ret = rsingleTag.exec( selector );

                    if ( ret ) {
                        if ( jQuery.isPlainObject( context ) ) {
                            selector = [ document.createElement( ret[1] ) ];
                            jQuery.fn.attr.call( selector, context, true );

                        } else {
                            selector = [ doc.createElement( ret[1] ) ];
                        }

                    } else {
                        ret = jQuery.buildFragment( [ match[1] ], [ doc ] );
                        selector = ( ret.cacheable ? jQuery.clone(ret.fragment) : ret.fragment ).childNodes;
                    }

                    return jQuery.merge( this, selector );

                // HANDLE: $("#id")
                } else {
                    elem = document.getElementById( match[2] );

                    // Check parentNode to catch when Blackberry 4.6 returns
                    // nodes that are no longer in the document #6963
                    if ( elem && elem.parentNode ) {
                        // Handle the case where IE and Opera return items
                        // by name instead of ID
                        if ( elem.id !== match[2] ) {
                            return rootjQuery.find( selector );
                        }

                        // Otherwise, we inject the element directly into the jQuery object
                        this.length = 1;
                        this[0] = elem;
                    }

                    this.context = document;
                    this.selector = selector;
                    return this;
                }

            // HANDLE: $(expr, $(...))
            } else if ( !context || context.jquery ) {
                return ( context || rootjQuery ).find( selector );

            // HANDLE: $(expr, context)
            // (which is just equivalent to: $(context).find(expr)
            } else {
                return this.constructor( context ).find( selector );
            }

        // HANDLE: $(function)
        // Shortcut for document ready
        } else if ( jQuery.isFunction( selector ) ) {
            return rootjQuery.ready( selector );
        }

        if ( selector.selector !== undefined ) {
            this.selector = selector.selector;
            this.context = selector.context;
        }

        return jQuery.makeArray( selector, this );
    },