title: Match with optional positive lookahead
body: <p>I've got 2 strings in the format:
  <code>Some_thing_here_1234 Match Me 1</code> &amp; <code>1234 Match Me 1_1</code></p>
  <p>In both cases I want the resultant match to be <code>1234 Match Me 1</code></p>
  <p>So far I've got <code>(?&lt;=^|_)\d{4}\s.+</code> which works but in the case of string 2 also captures the <code>_1</code> at the end. I thought I could use a lookahead at the end with an optional such as <code>(?&lt;=^|_)\d{4}\s.+(?=_\d{1}$|$)</code> but it always seems to revert to the second option and so the <code>_1</code> gets through.</p>
  <p>Any help would be great</p>