Default Element (BorderWidth) (RDL)
Specifies the default width of the border of the item.
Default contains an expression that evaluates to a string that contains a number (with a period character used as an optional decimal separator). The number must be followed by a designator for a CSS length unit such as cm, mm, in, pt, or pc. A space between the number and the designator is optional. For more information about size designators, see "CSS Length Units Reference" at msdn.microsoft.com. The value for the Default element must be between .25pt and 20pt.
The Default element can be overridden for a specific side through the Left, Right, Top, or Bottom elements. If borders overlap, the width of the border is determined by the rendering extension.