2.2.4.24.40 borderStyleID

A unique identifier for a border Style element (section 2.2.4.24.8) within the Styles collection (section 2.2.4.24.7).

The default worksheet cell border style is "bD".

 <s:simpleType name="borderStyleID" final="restriction">
   <s:restriction base="s:string">
     <s:pattern value="bD|\-[1-9][0-9]*" />
   </s:restriction>
 </s:simpleType>