title: How to validate a field of Zend_Form based on the value of another field?
body: <p>I'm trying to add a custom validator to a field. It should take into account the value of another field. E.g. field A should be at most B+50%.</p>
  
  <p>I've made a class implementing <code>Zend_Validate_Interface</code>, but apparently Zend Form only sends in the value of the current field to the validator. How do I make the validator receive everything?</p>