title: Clearing textbox makes it inaccessible
body: <p>See the atttached fiddle. I have a trial in which pressing buttons will place them into a textbox. I want users to be able to "start over" and hit the "clear" button to erase their answer. The clear button works, but afterwards, pressing other buttons does not put them back into the textbox as before.</p>
  
  <p>Current code for "clear" button:</p>
  
  <pre><code>function CLEAR(){
  letters.value = "";
  };
  </code></pre>
  
  <p><a href="https://jsfiddle.net/xxPoLyGLoTxx/ea6rnwLr/" rel="nofollow noreferrer">https://jsfiddle.net/xxPoLyGLoTxx/ea6rnwLr/</a></p>