title: What is fusion in Haskell?
body: <p>Every now and again I have been noticing the following in Haskell documentation:
  (for example in <a href="https://hackage.haskell.org/package/text-1.2.2.1/docs/Data-Text.html" rel="noreferrer"><code>Data.Text</code></a>):</p>
  
  <blockquote>
    <p>Subject to fusion</p>
  </blockquote>
  
  <p>What is <em>fusion</em> and how do I use it?</p>