title: Analyse logic of GXT FileUploadField
body: <p>GXT 3.x only.</p>
  
  <p>Could someone analyse and explain the connection between the three private fields in FileUploadField?</p>
  
  <p>Specifically,</p>
  
  <ol>
  <li>where is the onclick action of the button that would trigger fileinput display? If not where, then how.</li>
  <li>How does the fileinput.getValue() get transferred to the text input widget?</li>
  </ol>
  
  <p>If you could answer the above questions, you should be able to answer this one ... (but please don't answer this question if you do not provide answers to the above two questions). Is the following statement true, somewhat true or incidental?</p>
  
  <ul>
  <li>GXT has deliberately made it impossible to trigger button onclick programmatically because Security Concerns should not allow the file input element to be triggered programmatically.</li>
  <li>If that is true, (why?) I could still access the button and fileinput elements programmatically, anyway. There's no stopping me or anyone.</li>
  </ul>
  
  <p><strong>EDIT</strong><br>
  OK, never mind item 2: fileinput value is transferred to text input at onChange method.</p>