title: Weak Tables in lua - What are the practical uses?
body: <p>I understand what weak tables are.<br>
  But I'd like to know where weak tables can be used practically?</p>
  
  <p>The docs say</p>
  
  <blockquote>
    <p>Weak tables are often used in situations where you wish to annotate
    values without altering them.</p>
  </blockquote>
  
  <p>I don't understand that. What does that mean?</p>