title: How to highlight adjacent duplicate lines
body: <p>Is there a way to highlight duplicate lines in Vim, in a file, BUT only if they're <em>adjacent</em> to each other, i.e. if there is a line (in line 1) and there is a duplicate of that line (in line 99), do not highlight that.</p>
  
  <p>But if there is a line in (line n), and there is a duplicate of that line in lines (either, n-1 or n+1) highlight those (or just duplicates).</p>
  
  <p><em>Is it something regex can accomplish?</em></p>
  
  <p>(this is waaay off my regex skills)</p>