title: usage of import with plain header files
body: <p>Is it good practice to get rid of <code>#include</code> and only use the <code>import</code> keyword instead even for headers (like <code>&lt;span&gt;</code> or <code>&quot;Foo.h&quot;</code>)? Are there any benefits to this? Any possible downsides? Does it add to the length of build time?</p>
  <p><a href="https://en.cppreference.com/w/cpp/keyword/import" rel="nofollow noreferrer">cppreference</a> has an example in which it says this:</p>
  <blockquote>
  <p>import &lt;set&gt;; // imports a synthesized header unit formed from header </p>
  </blockquote>
  <p>What exactly does <em>synthesized</em> mean in this context?</p>