title: What is the "un-tab" sequence in (g)Vim?
body: <p>This is an annoyance I've had for a long time.</p>
  
  <p>(Nitpicky section: I prefer 4 space characters to tab characters.  It's a lot easier to type "tab" instead of explaining that.  When I say "tab", I mean "the action that happens when you press the tab key" which is probably more simply stated as "increase indentation".)</p>
  
  <p>I'm using smartindent while editing a document where indentation has some significance.  In "dumb" windows text editors I can press Shift+Tab to remove a tab or, more appropriately, decrease the indentation level of the current line.  I can't figure out how to do this from edit mode in Vim; Shift+Tab seems to count just the same as Tab.</p>
  
  <p>I know in Command mode <code>&lt;&lt;</code> will decrease indentation.  I want the equivalent in edit mode.  These are the solutions I've found so far and why I don't like them, one in particular may be the key to the answer.</p>
  
  <ol>
  <li>Use Notepad++ or some other dumb editor.  I've done this for a couple of years but I really miss Vim.</li>
  <li>Exit edit mode, use &lt;&lt;, enter edit mode.  This just puts the cursor at column 0; if I wanted this I wouldn't have tried smartindent.</li>
  <li>Stop using smartindent.  I don't decrease indent as often as I need to keep the same indent level; this would be a loss of productivity.</li>
  <li>The left arrow key seems to decrease the indent by one level.  I'd rather something I can do without leaving the home row.  This is the most promising choice.</li>
  </ol>
  
  <p>Maybe there's an option I can set?  Maybe I can rebind left arrow to something?  (If it requires rebinding please explain in detail; I've never delved into reconfiguring (g)Vim.</p>