- Most common usage today is RPC: send a method name and some parameters
    to a target object in order to get some result.
- Orthogonal use of the protocol: RPC module.
Example:
...
  <m:GetTemperature xmlns:m="http://example.org/weather">
    <city>Tokyo</city>
    <country>Japan</country>
  </m:GetTemperature>
...