Dom层次关系图:
windows(代表浏览器)
|____location
|____frames
|____history
|____navigator
|____screen
|____document
|__links
|__anchors
|__images
|__filters
|__forms
|__applets
|__embeds
|__plusins
|__frames
|__ncipts
|__all
|__selection
|__styleSheets
|__body
windows(代表浏览器)
|____location
|____frames
|____history
|____navigator
|____screen
|____document
|__links
|__anchors
|__images
|__filters
|__forms
|__applets
|__embeds
|__plusins
|__frames
|__ncipts
|__all
|__selection
|__styleSheets
|__body