Clears positioning back to the default when the document was loaded.
@param {String} [value=''] The value to use for the left, right, top, bottom.
You could use 'auto'.
@return {Ext.dom.Element} this
function(value) {
            value = value || '';
            return this.setStyle({
                left : value,
                right : value,
                top : value,
                bottom : value,
                'z-index' : '',
                position : STATIC
            });
        }