simpleType  thickness  
version  
namespace http://www.w3.org/1998/Math/MathML
type restriction of xsd:string 
used by
attribute     {}:mfrac.attlist/@linethickness {}:mstyle.attlist/@linethickness 
source <xsd:simpleType  name="thickness">
<xsd:restriction  base="xs:string">
<xsd:enumeration  value="thin">
</xsd:enumeration> <xsd:enumeration  value="medium">
</xsd:enumeration> <xsd:enumeration  value="thick">
</xsd:enumeration>
</xsd:restriction>
</xsd:simpleType>