title: Display error when entire form is blank in CodeIgniter
body: <p>I'm trying to create a fairly simple form that has a few checkboxes and input fields and a textarea.  Nothing is required by itself; however, if 'A' checkbox is checked, then 'A' input field is required (and so on for the couple other checkboxes I have).</p>
  
  <p>I have the above functionality in place, but I'm having a tough time figuring out how to have an error returned if the form is submitted blank (since nothing is required by default).</p>
  
  <p>Does anyone know of an easy-ish solution for this?  It seems like it should be so simple...</p>
  
  <p>Thanks</p>