title: ERROR: invalid regular expression: quantifier operand invalid
body: <p>I am trying to write a regular expression to get the "url" from the following text: </p>
  
  <pre><code>[![title](thumbnail_url?height=240&amp;width=320)](url)
  </code></pre>
  
  <p>using the following postgresql query:</p>
  
  <pre><code>SELECT (SELECT m[1] FROM regexp_matches(text, '^\[\!\[^*\]\(^ *\)\]\(((^*))') AS r(m) LIMIT 1) FROM texts;
  </code></pre>
  
  <p>I am getting the following error while I execute the above query:</p>
  
  <pre><code>ERROR:  invalid regular expression: quantifier operand invalid
  </code></pre>