Setting of display border for various part of the page such as PageSkin, ContentSkin,ControlSkins, WebBox and TemplateSkins.。 if display, the corresponding part of the page will have red color border,so that it will be easy for you to see where controls(or Page, content) are located。
Default，no border will be displayed for various runmodel and only when you put a mouse over , the corresponding part of the page will have a border。