title: Yii framework validation rules
body: <p>I am using Yii 1 for my project. I have 5 fields in a form, which must be filled. There's no problem with that - a simple validation rule in model. However, there is one more field, which is not required. But if it is filled, other 5 fields must become not-required. How should I define such validation rules in rules() method in model?</p>
  
  <p>Thank you in advance very much!</p>