I've had a couple occasions now where having the key of the map node
(or index for sequence) would have been very helpful in the my type
defs

  ---
  a: !!table
    ...

  YAML.add_private_type('table') { |tag, data|
    Table.new( key, data)  # have no key
  }

  class Table
    def initialize( name, data )
      @name = name  # needs to be 'a'
      ...

Might that be possible in the future -- I imagine you'd hav to pass the
node type too seq or map.

Thanks,
T.