title: Regex: only alphanumeric but not if this is pure numeric
body: <p>For instance:</p>
  
  <pre><code>'1'     =&gt; NG
  '243'   =&gt; NG
  '1av'   =&gt; OK
  'pRo'   =&gt; OK
  '123k%' =&gt; NG
  </code></pre>
  
  <p>I tried with</p>
  
  <pre><code> /^(?=^[^0-9]*$)(?=[a-zA-Z0-9]+)$/
  </code></pre>
  
  <p>but it is not working very well.</p>