A SOAP Envelope at it's simplest implementation. This envelope defines that it is a SOAP message, with a single method called 'echoString', which is given a single parameter, 'inputString'.

SOAP Envelope
<Envelope xmlns="http://schemas.xmlsoap.org/soap/envelope/">
  <Body>
    <method:echoString xmlns:method="http://soapinterop.org/">
      <inputString>hello world!</inputString>
    </method:echoString>
  </Body>
</Envelope>