gistfile1.rbx

class Doc
  def method_missing(m, *args, &block)
    args.empty? ? options[m] : options[m] = args[0]
  end
  def options
    @options ||= {}
  end
  def initialize(&block)
    self.instance_eval(&block) if block
  end
end

d = Doc.new do
  hi "you"
  mydoc(Doc.new do
    who "me"
  end)
end
# When instance evaluating within the d Doc, hi is sent "you" as args
#  but inside the block, mydoc's who is NOT sent "me." Instead, it is 
#  sent nil

puts d.hi # => you
puts d.mydoc # => #<Doc:0x338308>
puts d.mydoc.who # => nil ?