title: What's the standard for XML-RPC fault codes?
body: <p>In the process of writing a pingback handler for my website, I noticed that the <a href="http://www.xmlrpc.com/spec" rel="nofollow noreferrer">XML-RPC specification</a> doesn't say anything about what fault codes should be defined and what they should mean. So the question is, is there a commonly accepted standard for fault codes that specifies this information? Which fault codes are defined and what do they mean? Both for XML-RPC in general, and for specific applications (like pingback)?</p>
  
  <p>I think I know an answer to this but I'd like to get the community's input on it (and I think it's good reference material to have on SO).</p>