title: What is a formal definition of a first responder in iOS?
body: <p>I understand that a first responder object is the receives a callback signal according to input activity, etc and that it will bubble it up the chain until a responder willing to handle it can be found.  </p>
  
  <p>But more formally, what is the scope of the first responder?  For instance, is it an application-wide responder?  It seems like being a first responder is simply saying that this particular object will receive notification of interaction.  Can another responder steal the first responder status?</p>
  
  <p>Please explain or direct me to some pertinent information.  I've read Apple's general explanation of what a responder is.  I'm looking for an explanation that's little more built out.</p>