AWS S3 CORS XML RelaxNG schema

cors-xml-schema.rng.xml

<element name="CORSConfiguration" xmlns="http://relaxng.org/ns/structure/1.0">
  <oneOrMore>
    <element name="CORSRule">
      <interleave>
        <oneOrMore>
          <element name="AllowedOrigin"><text /></element>
        </oneOrMore>
        <oneOrMore>
          <element name="AllowedMethod">
            <choice>
              <value>GET</value>
              <value>PUT</value>
              <value>POST</value>
              <value>DELETE</value>
              <value>HEAD</value>
            </choice>
          </element>
        </oneOrMore>
        <zeroOrMore>
          <element name="AllowedHeader"><text /></element>
        </zeroOrMore>
        <zeroOrMore>
          <element name="ExposeHeader"><text /></element>
        </zeroOrMore>
        <optional>
          <element name="MaxAgeSeconds">
            <data type="nonNegativeInteger" datatypeLibrary="http://www.w3.org/2001/XMLSchema-datatypes"/>
          </element>
        </optional>
        <optional>
          <element name="ID"><text /></element>
        </optional>
      </interleave>
    </element>
  </oneOrMore>
</element>

Looks good to me!
You can also add the optional "ID" element, which is an arbitrary string up to 255 chars that identifies a rule.

The closest thing I can find to a schema is the table in http://docs.aws.amazon.com/AmazonS3/latest/API/RESTBucketPUTcors.html, which is not in any sort of schema form.

Thanks for the feedback Lincoln! I've updated the schema to add the optional ID element, and I modified the MaxAgeSeconds datatype from integer to nonNegativeInteger