# The `XMLTag` children with the `tag_name`
	#
	# ~~~
	# var code = """
	# <?xml version="1.0" encoding="us-ascii"?>
	# <animal>
	#     <cat/>
	#     <tiger>This is a white tiger!</tiger>
	#     <cat/>
	# </animal>"""
	#
	# var xml = code.to_xml
	# assert xml["animal"].length == 1
	# assert xml["animal"].first["cat"].length == 2
	# ~~~
	fun [](tag_name: String): Array[XMLTag]
	do
		var res = new Array[XMLTag]
		for child in children do
			if child isa XMLTag and child.tag_name == tag_name then
				res.add child
			end
		end
		return res
	end