title: Exclude expressin '?!' cannot be validated
body: <p>In my xsd schema, there is one particular regex <code>&lt;xs:pattern value="(?!TR)[A-Z]{2}"/&gt;</code> pattern which causes an error. I want just ignore 'TR' and match all other country codes. Although the regular expression works fine in several online editors, Eclipse says:</p>
  
  <blockquote>
    <p>InvalidRegex: Pattern value '(?!TR)[A-Z]{2}' is not a valid regular expression. The reported error was: 'This expression is not supported in the current option setting.'</p>
  </blockquote>
  
  <p>Despite it's a simple expression, cannot figure that out why it cannot be validated. With this error, I cannot deploy xsd file to the service bus. Is there a problem about aclipse itself or sth else?</p>
  
  <p>all advises are much appreciated!</p>
  
  <p><img src="https://i.stack.imgur.com/Jn42D.png" alt="it works as desired"></p>