# File lib/action_dispatch/middleware/best_standards_support.rb, line 16
    def call(env)
      status, headers, body = @app.call(env)

      if headers["X-UA-Compatible"] && @header
        unless headers["X-UA-Compatible"][@header]
          headers["X-UA-Compatible"] << "," << @header.to_s
        end
      else
        headers["X-UA-Compatible"] = @header
      end

      [status, headers, body]
    end