If the user attempts to switch tab stops while the cursor is not *on* a tab stop, the snippet is terminated

src/app/anchor-range.coffee

@@ -16,6 +16,9 @@ class AnchorRange
   getScreenRange: ->
     new Range(@startAnchor.getScreenPosition(), @endAnchor.getScreenPosition())
 
+  containsBufferPosition: (bufferPosition) ->
+    @getBufferRange().containsPoint(bufferPosition)
+
   destroy: ->
     @startAnchor.destroy()
     @endAnchor.destroy()