               # in the future, we could replace the cursors, with a y-selections
               #
               window.setTimeout(()->
-                  event.object.delete(author)
+                  event.object.delete(authorId)
                 , 0)
               return
             else

    @_model.getContent("cursors").observe (events) => @locker.try ()=>
      for event in events
        if event.type is "update" or event.type is "add"
          author = event.changedBy
          ref_to_char = event.object.val(author)
          if ref_to_char is null
            position = @editor.getLength()
          else if ref_to_char?

            console.warn "ref_to_char is undefined"
            return

          # never knows…
          if authorId == "length"
            authorId = "_length"
          if authorId in @_colors
            color = @_colors[authorId]
          else
            @_colors.length++
            color = @_graphicsPalette[@_colors.length%@_graphicsPalette.length]
            @_colors[authorId]

          params =
            id: author
            index: position
            text: author(authorId)
            color: "grey"
          @editor.setCursor params
        else
