title: Sublime Text 2: How to Page Up/Down without moving the cursor
body: <p>I'm on OS X 10.8.4 using ST2. When I use the Home and End keys, the viewport moves and the cursor is left alone. This is standard Mac behavior, and what I'd expect.</p>
  
  <p>However, when I use Page Up (pageup/pgup) and Page Down (pagedown/pgdn), the cursor moves along with the viewport. This is not how other Mac apps behave, and I'd like the cursor to be left alone for these keys too.</p>
  
  <p>I've been able to get this half-working by adding this to my key bindings:</p>
  
  <pre><code>[
     { "keys": ["pageup"], "command": "scroll_lines", "args" : {"amount": 30.0} },
     { "keys": ["pagedown"], "command": "scroll_lines", "args" : {"amount": -30.0} }
  ]
  </code></pre>
  
  <p>However, the amounts there are hard-coded. It looks like viewport_extent will get me the height of the viewport, but how can I use that from within the key bindings file? Is this even the correct solution for this? I feel like it's an awful lot of work to go to to get this behavior.</p>
  
  <p>Thanks in advance.</p>