     if head.type is 'newline'
       return false
 
+    # `key` is a unique identifier for this
+    # mark, to be used later for removal
     key = @markedBlockKey++
 
     @markedBlocks[key] = {

        path = @getHighlightPath info.model, info.style
        path.draw @highlightCtx
      else
        delete @markedLines[line]

    for id, info of @extraMarks
      if @inTree info.model


    @redrawHighlights()

    # Return `key`, so that the caller can
    # remove the line mark later with unmark(key)
    return key

  Editor::unmark = (key) ->
