Description

i had the need to get the visible window width & height. (to ensure an element won't be positioned outside this range)

getting these values depends heaviliy on the browser you are using. so i added two attributes to Position, which get initialized on Position.prepare (in most cases you need this you will call Position.prepare anyway, because you need also scrollX/Y, resp. deltaX/Y)

maybe that is also useful for others and makes it into prototype.js

!!! i haven't (couln't) test it on Safari.

var Position = {
  // ...
  prepare: function() {
    // ...
    this.visibleWidth = 
        (window.opera) ? document.body.clientWidth || document.documentElement.clientWidth || window.innerWidth
        : document.documentElement.clientWidth || window.innerWidth || document.body.clientWidth;
    this.visibleHeight = 
        (window.opera) ? document.body.clientHeight || document.documentElement.clientHeight || window.innerHeight
        : document.documentElement.clientHeight || window.innerHeight || document.body.clientHeight;
    // ...