title: Non-capturing lookbehind regex match is not working
body: <p>Problem statement is as follows.</p>
  
  <p>my description is </p>
  
  <p>abc abcxxyz 10xabc abcx10 abc10xabc abcx10xyz</p>
  
  <p>want the regex which will match abc only if it is preceded by digit + x or succeeded by x + digit.</p>
  
  <p>In above example it should match abc from abcx10 , 10xabc and abcx10xyz
  but should not capture digits in those matches.
  that means while replacing text it should replace only abcx or xabc.</p>
  
  <p>Have tried <code>(((((?:\d+)))[Xx]))(abc)(\s|$|(([Xx](?=((\d).)+)))|[^a-zA-Z0-9])</code> but it is not excluding digits from capturing. </p>
  
  <p>Thanks.</p>