title: What is the purpose of a UML Qualifier?
body: <p>I can't understand what a qualifier is in UML. 
  For example, in the scanned page, there's a qualifier named
  "SharedRegister" that has "state" and "plateNumber" in it.</p>
  
  <p>Why not just used a class called SharerRegister and put "state"
  and "plateNumber" in it? What does it offer over a class exactly?</p>
  
  <p><img src="https://i.stack.imgur.com/o4ShI.jpg" alt="Schaum UML - pg 108"></p>
  
  <p>(Image from Schaum's Outlines, UML 2nd edition. Simon Benett. Pg 108)</p>