manila/manila/api/schemas/v1.1/metadata.rng

  <element name="metadata" ns="http://docs.openstack.org/compute/api/v1.1"
    xmlns="http://relaxng.org/ns/structure/1.0">
    <zeroOrMore>
      <element name="meta">
        <attribute name="key"> <text/> </attribute>
        <text/>
      </element>
    </zeroOrMore>
  </element>