# File lib/sinatra/respond_to.rb, line 169 def format(val=nil) unless val.nil? mime_type = ::Sinatra::Base.mime_type(val) fail "Unknown media type #{val}\nTry registering the extension with a mime type" if mime_type.nil? @_format = val.to_sym response['Content-Type'].sub!(/^[^;]+/, mime_type) end @_format end