title: Placeholder for UITextView
body: <p>Anyone ever implements something in UITextView that stopping it from receiving future inputs when the text length is smaller than certain threshold? I plan to implement a textview like we have in the mail composer interface. We have a placeholder "Subject" there, and the cursor starts after. </p>
  
  <p><a href="https://stackoverflow.com/questions/1328638/placeholder-in-uitextview">Placeholder in UITextView</a>
  Inspired from this question, I wonder if there are some methods which could be used to stop changing the text in the UITextView once the cursor is moving back to the placeholder string.</p>
  
  <p>Any ideas?</p>