title: Standard for adding multiple values of a single HTTP Header to a request or response
body: <p>If I want to add a list of values as an HTTP Header, is there a standard way to do this?  I couldn't find anything (that I could easily understand) in RFC 822.  For example, is
  comma separated values standard or semi-colon separated values.  Is there a standard at all?</p>
  
  <p>Example:</p>
  
  <pre><code>Key: value1;value2;value3
  </code></pre>