jquery 1.7和1.9的position方法对固定(fixed)元素的区别

在jquery的position方法，官方是这样说明的：

Get the current coordinates of the first element in the set of matched elements, relative to the offset parent.The .position() method allows us to retrieve the current position of an element relative to the offset parent. Contrast this with .offset(), which retrieves the current position relative to the document. When positioning a new element near another one and within the same containing DOM element, .position() is the more useful.jQuery does not support getting the position coordinates of hidden elements or accounting for borders, margins, or padding set on the body element.

大致意思是获得匹配元素相对于最近定位父级的距离，返回left、top值。

关于这个区别，没有在官方的jquery升级指南里指出来，这里就抛钻引玉一下下啦。

jquery 1.9版本测试：