title: In Custom Configuration Sections, can you make a ConfigurationProperty required if another ConfigurationProperty is set to a certain value?
body: <p>I would like to try and enforce a configuration property's existence if another configuration property exists that is set to a certain value.</p>
  
  <p>For example, if this is my <a href="http://msdn.microsoft.com/en-us/library/2tw134k3%28v=vs.100%29.aspx" rel="nofollow">Custom Configuration Section</a>:</p>
  
  <pre><code>&lt;CustomSettingsSection&gt;
    &lt;Action ActionType="SendEmail" FromAddress="SomeEmailAddress"/&gt;
    &lt;Action ActionType="LogToFile"/&gt;
  &lt;/CustomSettingsSection&gt;
  </code></pre>
  
  <p>I would like to make it so that the user must always specify a FromAddress whenever the ActionType is set to SendEmail, otherwise I do not require they specify the FromAddress, as not specifying the FromAddress on an ActionType of LogToFile is logically unnecessary. </p>