# 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