title: Are character set names case-sensitive in HTTP?
body: <p>This is a follow-up to <a href="https://stackoverflow.com/q/5258977/1497596">Are HTTP headers case-sensitive?</a>.</p>
  
  <p>In the HTTP <code>Content-Type</code> header, I have seen character set names expressed both in upper- and lower-case form. For example, for the <code>UTF-8</code> character set:</p>
  
  <pre><code>Content-Type: text/html; charset=UTF-8
  
  Content-Type: text/html; charset=utf-8
  </code></pre>
  
  <p>Here are some mixed-case variants <em>(the latter two certainly not being likely in the real world)</em>:</p>
  
  <pre><code>Content-Type: text/html; charset=Utf-8
  
  Content-Type: text/html; charset=UtF-8
  
  Content-Type: text/html; charset=uTf-8
  </code></pre>
  
  <p>Are all forms equally valid? Or, are the client and server applications that ignore the case of the character set name merely being flexible? Alternatively, are those applications that recognize only one representation non-compliant?</p>