title: lua gsub %b <-- how does this work?
body: <p>In the following lua code:</p>
  
  <pre><code>function interp(s, tab)
    return (s:gsub('($%b{})', function(w) return tab[w:sub(3, -2)] or w end))
  end
  </code></pre>
  
  <p>what does the %b mean?</p>
  
  <p>and how does this match stuff like "${name}" ?</p>