P5: Guidelines for Electronic Text Encoding and Interchange

<rng:define name="data.sex">
 <rng:choice>
  <rng:value>0</rng:value>
  <rng:value>1</rng:value>
  <rng:value>2</rng:value>
  <rng:value>9</rng:value>
 </rng:choice>
</rng:define>

data.sex = "0" | "1" | "2" | "9"