P5: Guidelines for Electronic Text Encoding and Interchange

<rng:element name="variantEncoding">
 <rng:ref name="att.global.attributes"/>
 <rng:attribute name="method">
  <rng:choice>
   <rng:value>location-referenced</rng:value>
   <rng:value>double-end-point</rng:value>
   <rng:value>parallel-segmentation</rng:value>
  </rng:choice>
 </rng:attribute>
 <rng:attribute name="location">
  <rng:choice>
   <rng:value>internal</rng:value>
   <rng:value>external</rng:value>
  </rng:choice>
 </rng:attribute>
 <rng:empty/>
</rng:element>

element variantEncoding
{
   att.global.attributes,
   attribute method
   {
      "location-referenced" | "double-end-point" | "parallel-segmentation"
   },
   attribute location { "internal" | "external" },
   empty
}