title: What's the "Content-Length" field in HTTP header?
body: <p>What does it mean?</p>
  
  <ol>
  <li>Byte count of encoded content string with encoding specified in header.</li>
  <li>Character count of content string.</li>
  </ol>
  
  <p>Especially in case of <code>Content-Type: application/x-www-form-urlencoded</code>.</p>