title: XSD pattern character evaluation
body: <p>I am looking at the XSD regex pattern here: <code>&lt;xsd:pattern value="[0-9]{0,3}[C,T]{0,1}"/&gt;</code> (From <a href="http://www.fly.faa.gov/ASDI/asdidocs/NasXCoreElements.xsd" rel="nofollow">http://www.fly.faa.gov/ASDI/asdidocs/NasXCoreElements.xsd</a> on line 1747) The <code>[C,T]</code> component really confuses me in particular. What is the <code>,</code> for in the middle of the character set evaluation? I cannot find what this type of expression does anywhere.</p>
  
  <p>I have some ideas on what this might do:</p>
  
  <ol>
  <li>Evaluates the <code>,</code> character as part of the expression (this would be strange as <code>,</code> is not an altitude specifier the regex is attempting to evaluate for)</li>
  <li>The <code>,</code> is some special range specifier?</li>
  </ol>