title: What does the tsconfig option "lib" do?
body: <p>I have an existing project that has this line in tsconfig.json:</p>
  
  <pre><code>lib:["2016", "DOM"]
  </code></pre>
  
  <p>What is the purpose of this?</p>
  
  <p>The only info I could find is this:</p>
  
  <blockquote>
    <p>Specify library file to be included in the compilation. Requires
    TypeScript version 2.0 or later.</p>
  </blockquote>
  
  <p>What does that mean?</p>