title: Zend Framework: setting a Zend_Form_Element form field to be required, how do I change the validator used to ensure that the element is not blank
body: <p>When using a <code>Zend_Form</code>, the only way to validate that an input is not left blank is to do</p>
  
  <pre><code>$element-&gt;setRequired(true);
  </code></pre>
  
  <p>If this is not set and the element is blank, it appears to me that validation is not run on the element.</p>
  
  <p>If I do use <code>setRequired()</code>, the element is automatically given the standard NotEmpty validator. The thing is that the error message with this validator sucks, "Value is empty, but a non-empty value is required". I want to change this message. At the moment I have done this by changing the <code>Zend_Validate_NotEmpty</code> class, but this is a bit hacky.</p>
  
  <p>I would ideally like to be able to use my own class (derived from <code>Zend_Validate_NotEmpty</code>) to perform the not empty check.</p>