title: How golang replace string by regex group?
body: <p>I want to use regex group to replace string in <code>golang</code>, just like as follow in <code>python</code>:</p>
  
  <pre><code>re.sub(r"(\d.*?)[a-z]+(\d.*?)", r"\1 \2", "123abc123") # python code
  </code></pre>
  
  <p>So how do I implement this in golang?</p>