The source code

    	Ext.lib.Region = function(t, r, b, l) {
    		var me = this;
            me.top = t;
            me[1] = t;
            me.right = r;
            me.bottom = b;
            me.left = l;
            me[0] = l;
        };

        Ext.lib.Region.prototype = {
            contains : function(region) {
    	        var me = this;
                return ( region.left >= me.left &&
                         region.right <= me.right &&
                         region.top >= me.top &&
                         region.bottom <= me.bottom );

            },

            getArea : function() {
    	        var me = this;
                return ( (me.bottom - me.top) * (me.right - me.left) );
            },

            intersect : function(region) {
                var me = this,
                	t = Math.max(me.top, region.top),
                	r = Math.min(me.right, region.right),
                	b = Math.min(me.bottom, region.bottom),
                	l = Math.max(me.left, region.left);

                if (b >= t && r >= l) {
                    return new Ext.lib.Region(t, r, b, l);
                }
            },

            union : function(region) {
    	        var me = this,
                	t = Math.min(me.top, region.top),
                	r = Math.max(me.right, region.right),
                	b = Math.max(me.bottom, region.bottom),
                	l = Math.min(me.left, region.left);

                return new Ext.lib.Region(t, r, b, l);
            },

            constrainTo : function(r) {
    	        var me = this;
                me.top = me.top.constrain(r.top, r.bottom);
                me.bottom = me.bottom.constrain(r.top, r.bottom);
                me.left = me.left.constrain(r.left, r.right);
                me.right = me.right.constrain(r.left, r.right);
                return me;
            },

            adjust : function(t, l, b, r) {
    	        var me = this;
                me.top += t;
                me.left += l;
                me.right += r;
                me.bottom += b;
                return me;
            }
        };

        Ext.lib.Region.getRegion = function(el) {
            var p = Ext.lib.Dom.getXY(el),
            	t = p[1],
            	r = p[0] + el.offsetWidth,
            	b = p[1] + el.offsetHeight,
            	l = p[0];

            return new Ext.lib.Region(t, r, b, l);
        };