title: Qt Validators - how do I reject intermediate results?
body: <p>As far as I understand, a validator can return three results: Invalid, Intermediate and Acceptable.
  Suppose my line edit has a regexp validator set with the following regular expression:</p>
  
  <pre><code>[ab][cd]
  </code></pre>
  
  <p>So, valid values are: <code>ac</code>, <code>ad</code>, <code>bc</code>, <code>bd</code>:</p>
  
  <p>If I try to enter any other character, such as <code>e</code> or <code>0</code>, the line edit will not let me enter it physically. However, if I enter <code>a</code> and switch to another control, it will have no problems with it, although the value <code>a</code> is not acceptable, but rather, intermediate.</p>
  
  <p>Here's what I am after. I want the line edit to refuse me to switch focus to any other control if its input is not acceptable. That is, I need to enter a line which fully satisfies my regular expression so that I can switch focus. Otherwise I want my form/dialog etc to refuse me the ability to switch focus.</p>
  
  <p>Is there a straightforward one-liner way to do this or do I have to do this manually? If the latter, what's the standard way of doing this?</p>