static/ext/src/dom/Element_style.js
function(width) {
        var me = this,
            isNum = (typeof width == 'number');

        if (isNum && me.autoBoxAdjust && !me.isBorderBox()) {
            width -= (me.getBorderWidth("lr") + me.getPadding("lr"));
        }
        return (isNum && width < 0) ? 0 : width;
    }
function(width) {
        var me = this,
            isNum = (typeof width == 'number');

        if (isNum && me.autoBoxAdjust && !me.isBorderBox()) {
            width -= (me.getBorderWidth("lr") + me.getPadding("lr"));
        }
        return (isNum && width < 0) ? 0 : width;
    }
TODO: Look at this private  ==> used by Fx