gistfile1.txt

<validator class="or">
  <validators>
    <validator class="number" required="false">
      <argument>foo</argument>
      <error>not valid number</error>
    </validator>
    <validator class="number" required="false">
      <argument>bar</argument>
      <error>not valid number</error>
    </validator>
  </validators>
  <error>Give either foo or bar</error>
</validator>