# Allow an application to register an error event handler.
	#
	# If the application does not register an error handler, all
	# error events reported by the SAX parser will be silently
	# ignored; however, normal processing may not continue. It is
	# highly recommended that all SAX applications implement an
	# error handler to avoid unexpected bugs.
	#
	# Applications may register a new or different handler in the
	# middle of a parse, and the SAX parser must begin using the new
	# handler immediately.
	fun error_handler=(handler: nullable ErrorHandler) is abstract