title: Regex expression for start with 2 * is not allowed
body: <p>I would like to know the regex for not allowing string like</p>
  
  <pre><code>**Test
  </code></pre>
  
  <p>but string like </p>
  
  <pre><code>*test, test,123, 
  </code></pre>
  
  <p>is allowed. 
  So basically start with 2 Asterix(*) is not allowed rest everything is allowed.</p>
  
  <p>I have tried following regex expression</p>
  
  <p><code>[^(\*{2})].*
  [^(\*\*)].*
  [^(\*\*)$].*
  ^(?!\*\*.*)</code></p>