title: What is a role in a QTreeWidgetItem?
body: <p>I have a <code>QTreeWidget</code> with several Columns, I add <code>QTreeWidgetItems</code> to it. I try to make the second column contain a numerical value for each <code>Item</code> so I can sort the items by this value</p>
  
  <pre><code>QTreeWidgetItem has a method called setData(int column, int role, QVariant(data))
  </code></pre>
  
  <p>I cannot find any documentation on what this <code>role</code> argument is. All I know is that if I set it to 1 or 2, something shows up in the column, if I set it to 0 or >=3, nothing shows up in the column, regardless, the numbers always end up being sorted alphabetically, which is wrong.</p>