# Receive notification of a processing instruction.
	#
	# The Parser will invoke this method once for each processing
	# instruction found: note that processing instructions may occur
	# before or after the main document element.
	#
	# A SAX parser must never report an XML declaration (XML 1.0,
	# section 2.8) or a text declaration (XML 1.0, section 4.3.1)
	# using this method.
	#
	# Parameters:
	#
	# * `target`: processing instruction target.
	# * `data`: processing instruction data, or `null` if
	# none was supplied. The data does not include any
	# whitespace separating it from the target.
	fun processing_instruction(target: String, data: nullable String) do end