title: Regex to check when a word pattern is missing from the string
body: <p>I have a target string something like this 
  PT_content:data1 AND PT_content2:data2 OR PT_content3:data3</p>
  
  <p>now i need to check whether any invalid qualifier is there in the string., 
  For example </p>
  
  <p>PT_content:data1 AND PR_content2:data2 OR PT_content3:data3(this is invalid as only <strong>PT_xxxxxx:data</strong> is allowed.) </p>
  
  <p>I tried some pattern with negative lookahead, but it doesnt seem s to work</p>
  
  <pre><code>Pattern.compile("(?!.*PT_[a-zA-Z]*:)")
  </code></pre>
  
  <p>Thanks </p>