# Return the column number where the current document event ends.
	#
	# The number is one-based.
	#
	# **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.
	# For example, when lines contain combining character sequences, wide
	# characters, surrogate pairs, or bi-directional text, the value may
	# not correspond to the column in a text editor's display.
	#
	# The return value is an approximation of the column 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 column in each line is column 1.
	#
	# Return -1 in absence of column number.
	fun column_number: Int is abstract