when there is a DTD declaration, document.body.scrollTop is 0st document. DocumentElement.scrollTop is the normal value.
The height ofdocument.documentElement.clientHeight is the height of the display area.
html is that the height of the root node containing body,body is stretched by the element, so why isn"t html? It"s an immutable value.
when you move the scroll bar, the part beyond the visual area is exactly equal to the scrolling distance, but the height of the documentElement is always the same. If you keep scrolling the scroll bar. The scroll bar moves an infinite distance. Must be larger than the size of the visible area. So why is documentElement equivalent to document.body?