title: RegEx - Exclude char sequence from matches
body: <p>I'm struggeling with a RegEx and hope to find some guidance here. I already took a search on here and on Google, but it's hard for me to find the right terms. I could image that non-capturing groups would help me, but I don't know how to apply them.</p>
  
  <p>Basically I want to <strong>find Java single line comments, which are "screaming"</strong> (no lower case letters):</p>
  
  <pre><code>^[ \t]*//[^a-z]+?$
  </code></pre>
  
  <p>Now I also find comments like these:</p>
  
  <pre><code>// PN-123456 
  // ITK 12345
  //IT-12345
  </code></pre>
  
  <p><strong>These comments are valid</strong> for me, so I wanted to <strong>exclude them from the RegEx above</strong>. It's always this pattern:</p>
  
  <ol>
  <li>Optional whitespace</li>
  <li>"PN" or "IT" or "ITK"</li>
  <li>Hyphen, whitespace or nothing</li>
  <li>Four to six digits</li>
  <li>Optional whitespace</li>
  </ol>
  
  <p>That's my approach for this pattern:</p>
  
  <pre><code>[ ]?PN[ -]?[0-9]{1,6}
  </code></pre>
  
  <p>But now I just can't unite both expressions in one RegEx. How would this work?</p>
  
  <p>TIA,
  Peter</p>