class Rack::Config

end<br>env = ‘some-value’
use Rack::Config do |env|
Example:
initialization.
Rack::Config modifies the environment using the block given during

def call(env) 

def call(env)
  @block.call(env)
  @app.call(env)
end

def initialize(app, &block) 

def initialize(app, &block)
  @app = app
  @block = block
end