original App.config

<?xml version="1.0" encoding="utf-8" ?>
<configuration>
  <configSections>
    <section name="example" type="CustomConfig.ExampleSection,
                                 CustomConfig" />
  </configSections>

  <example
    version="A sample string value."
  />

  <appSettings>
    <add key="version_string" value="1.01" />
  </appSettings>

</configuration>