title: How to replace within a capture group
body: <p>I am modifying an existing HTML doc. I'm doing things like adding a table of contents etc.</p>
  
  <p>I have a heading with this ID: <code>id="transcending intellectual limitations"</code> (for real!)</p>
  
  <p>I want to be able to find the whole ID, and then replace the spaces with hyphens.</p>
  
  <p>It would be simple if I had just the IDs but I don't want to remove all the spaces in the whole document.</p>
  
  <p>I'm reasonably new to regex, I'm using Sublime's find and replace to do this.</p>