title: Override or overload AutoComplete Append rule
body: <p>I have a textbox which sends some commands to an instrument. I added the AutoComplete feature to this textbox and things are going easier now.</p>
  
  <p>What I am thinking to improve this, is to add a possibility that when user enters a command (just a text) while AutoComplete finds a match it also shows a description for that command.</p>
  
  <p>At the moment, I have all the AutoComplete strings in a text file and I load it when the application starts. The textfile contains lines like this:</p>
  
  <pre><code>*IDN?   #Query the instrument for identification
  *RST    #Resets the instrument
  </code></pre>
  
  <p>So what is happening in my application is that because AutoComplete is in <code>SuggestAppend</code> mode, the description of command also gets into the textbox (this will be the same if I only put it in <code>Suggest</code> mode)</p>
  
  <p>What I need to know is how to force the AutoComplete to append the text while its</p>
  
  <ol>
  <li>Does not add any text starting from <code>#</code> char while appending the suggested text</li>
  <li>Trim() the text to avoid that spaces you see in the textfile source</li>
  </ol>
  
  <p><strong>UPDATE 1</strong>
  Ok, I think the only way is to make a new class and inherit from <code>AutoCompleteStringCollection</code> And in this new class, somehow override the reponsible method for returning (appending) suggested text. I really have no idea what should I do:</p>
  
  <pre><code>class MyAutoCompleteCollection : AutoCompleteStringCollection 
  {
      //How to override Get function of AutoCompleteStringCollection class?
      //It is not avilable to override :(
  }
  </code></pre>
  
  <p><strong>UPDATE 2</strong>
  I found out that methods in <code>AutoCompleteStringCollection</code>are not overridable. I am looking for a way to change the way the <code>[]</code> method (to be honest I do not know what to call it!) works. Does someone have any idea about this?</p>
  
  <p><img src="https://i.stack.imgur.com/YCBlZ.png" alt="enter image description here"></p>
  
  <p><strong>UPDATE 3</strong>
  When the text without #DESC  goes into the textbox, I have a event handler for KeyDown which will transfer the command to the instrument. </p>