code: function accessor (data) {
        // Behave like a setter if an argument is provided.
        if (arguments.length === 1) {
          var json = JSON.stringify(data)
  
          if (no(json)) {
            throw new Error('JSON do not serialize data:' + data)
          }
  
          graph.data[accessorName] = data
        }
  
        // Always behave also like a getter.
        return graph.data[accessorName]
      }
docs: Accessor-like function.
  
  @param {*} data that JSON can serialize