title: regular expression to match exact string
body: <p>this is probably very simple, but I would like to match for</p>
  
  <pre><code>abc
  </code></pre>
  
  <p>and exclude</p>
  
  <pre><code>abcd
  </code></pre>
  
  <p>anything I try picks up both cases, but I only want the first. what regular expression ignored any case with abcd?</p>
  
  <p>thanks</p>