anchor.diff:  polyfillProperties = ->
     {prototype} = document.createElement("details").constructor
     {setAttribute, removeAttribute} = prototype
  -  setOpen = Object.getOwnPropertyDescriptor(prototype, "open")?.set
  -  getOpen = Object.getOwnPropertyDescriptor(prototype, "open")?.get
  +  open = Object.getOwnPropertyDescriptor(prototype, "open")
   
     Object.defineProperties prototype,
       open:
  
positive.code:         if @tagName is "DETAILS"
            @hasAttribute("open")
          else
            getOpen?.call(this)
        set: (value) ->
          if @tagName is "DETAILS"
            if value
  
negative.code:             @removeAttribute("open")
            value
          else
            open?.set?.call(this, value)
  
      setAttribute:
        value: (name, value) ->
  