# Return the line number where the current document event ends.
	#
	# Lines are delimited by line ends, which are defined in
	# the XML specification.
	#
	# **Warning:** The return value from this method
	# is intended only as an approximation for the sake of diagnostics;
	# it is not intended to provide sufficient information
	# to edit the character content of the original XML document.
	# In some cases, these "line" numbers match what would be displayed
	# as columns, and in others they may not match the source text
	# due to internal entity expansion.
	#
	# Return an approximation of the line number
	# in the document entity or external parsed entity where the
	# markup triggering the event appears.
	#
	# If possible, the SAX driver should provide the line position
	# of the first character after the text associated with the document
	# event. The first line is line 1.
	#
	# Return -1 in absence of line number.
	fun line_number: Int is abstract