title: BaseDir in app.config file, like WCF baseadress
body: <p>Hi would like to use an attribute within another attribute, like WCF baseadress.  My <code>app.config</code> file is like below. I've added a new section named BaseDir and then I would like to use it in an other section.</p>
  
  <pre><code> &lt;section name="BaseDir" type="System.Configuration.DictionarySectionHandler"/&gt;
   &lt;BaseDir&gt;
      &lt;add key="PreprocessorBase" value="C:\Users\MyUser\Desktop\FormProcessing\Preprocessor\"/&gt;
  &lt;/BaseDir&gt;
  </code></pre>
  
  <p>And then  I try to use it like below.</p>
  
  <pre><code>  &lt;Folders&gt;
      &lt;add key="FtpInput" value="${BaseDir.PreprocessorBase}Input\FtpInput"/&gt;
      &lt;add key="FtpBackup" value="${BaseDir.PreprocessorBase}Backup\FtpInput"/&gt;
  &lt;/Folders&gt;
  </code></pre>
  
  <p>Thanks.</p>