Any cross browser issues if I use document.documentElement ?
Target browsers are
You should have no problems: http://www.quirksmode.org/dom/w3c_core.html
Anyway here you have a test page: http://www.quirksmode.org/dom/tests/document.html#documentElement
Quirksmode says
document.documentElement.clientWidth/Height
http://duckduckgo.com/?q=!%20document.documentElement%20site%3Aquirksmode.org