class Sinatra::Base

def error(*codes, &block)

handled.
class, or an HTTP status code to specify which errors should be
Define a custom error handler. Optionally takes either an Exception 
def error(*codes, &block)
  args  = compile! "ERROR", /.*/, block
  codes = codes.flat_map(&method(:Array))
  codes << Exception if codes.empty?
  codes << Sinatra::NotFound if codes.include?(404)
  codes.each { |c| (@errors[c] ||= []) << args }
end