title: vim: multiple "sessions" in the same instance?
body: <p>I work on a growing project with vim. I like to have most of the project files open in the same session. However, as the project's growing, I start to have too many files open at the same time; switching between files <strong>[*]</strong> starts getting a bit unproductive at 40+ files because the list gets too long (for, say, 20 files this way of navigating works very well for me, however).</p>
  
  <p><strong>Is there a way to split the session in multiple "sub-sessions" in the same instance of vim?</strong></p>
  
  <p>How I imagine it is that each session would contain, say, 20 files and only list those with <code>:ls</code>, and that I could switch between them in the same vim window (basicallly the same as if I'd run multiple instances of vim in the same shell and switch between them with <code>Ctrl-Z; fg %X</code>, just without leaving vim).</p>
  
  <p><strong><em>[*]</strong> I like to navigate between files with <code>:ls</code> followed by <code>:bX</code> (or directly <code>:bX</code> in case I've memorized a buffer number), along with <code>:bp</code>/<code>:bn</code>, and I always have at least two split open, and this workflow works quite well for me, so I'm not looking for more efficient alternatives to <code>:ls</code>.</em></p>