How Sinatra avoids polluting inheritance chain

When you open a new file:

[13] pry(main)> self
=> main
[14] pry(main)> self.class
=> Object

main is an instance of Object

An example: the Sinatra DSL

require 'sinatra'

get '/' do
  'Hello world!'
end

#get is put in main's singleton class

[1] pry(main)> require 'sinatra'
=> true
[2] pry(main)> method(:get).source_location
=> .../sinatra-1.4.6/lib/sinatra/base.rb", 1987]
pry(main)> Object.new.get
NoMethodError: undefined method `get' for #<Object:0x007fc423d9ec18>

This is achieved by extending the singleton class of main.

from Sinatra:

extend Sinatra::Delegator

A simple example:

class Foo
  module DSL
    def foo
      'bar'
    end
  end
end

extend ::Foo::DSL