title: Bootstrap - Why: Row remove margin-left & not Row-fluid
body: <p><strong>Row :</strong> <code>margin-left: -20px;</code></p>
  
  <p><strong>Row-fluid :</strong> nothing about <code>margin-left</code>.</p>
  
  <p>Why row-fluid is not removing this <code>margin-left</code> by a certain <code>%</code> ?</p>
  
  <p><em>Edit :</em><br>
  <code>.row-fluid</code> > <code>.span</code> is adding <code>margin-left</code>.</p>