title: Handle "API usage limit" errors in eBay trading API
body: <p>While developing a trading application which proficiently handles API error conditions, I'm now focused on the class of API errors regarding usage limits.</p>
  
  <p>The <a href="http://developer.ebay.com/DevZone/XML/docs/Reference/ebay/Errors/ErrorMessages.htm" rel="nofollow">Trading API errors list</a> is far too extended to me; according to the list, we have the following error codes:</p>
  
  <ul>
  <li>error 518: Your application has exceeded usage limit on this call, [...]</li>
  <li>error 18000:  You have exceeded your daily request limit, therefore you will be unable to make additional requests for the remainder of the day.</li>
  <li>error 218050: Users of this application are limited to a number of calls they can make on a daily, hourly and 6-minute basis. [...]</li>
  <li>error 21919144: Maximum Call Limit Exceeded</li>
  <li>error 21919165: Maximum Call Limit Exceeded.</li>
  </ul>
  
  <p>I want to be sure which of these errors my application should handle automatically, if not all. I'm particularly worried if higher error code numbers could be less consolidated and more prone to change their meaning over future API versions.</p>
  
  <p>Worth considering, the Trading API errors list linked above doesn't contextualize the meaning of the errors, so their associated textual description could be misleading.</p>