# Report an attribute type declaration.
	#
	# Only the effective (first) declaration for an attribute will
	# be reported. The type will be one of the strings `CDATA`,
	# `ID`, `IDREF`, `IDREFS`, `NMTOKEN`, `NMTOKENS`, `ENTITY`,
	# `ENTITIES`, a parenthesized token group with
	# the separator `|` and all whitespace removed, or the word
	# `NOTATION` followed by a space followed by a parenthesized
	# token group with all whitespace removed.
	#
	# The value will be the value as reported to applications,
	# appropriately normalized and with entity and character
	# references expanded.
	#
	# Parameters:
	#
	# * `element_name`: name of the associated element.
	# * `attribute_name`: name of the attribute.
	# * `attribute_type`: string representing the attribute type.
	# * `mode`: string representing the attribute defaulting mode (`#IMPLIED`,
	# `#REQUIRED`, or `#FIXED`) or `null` if none of these applies.
	# * `value`: string representing the attribute's default value,
	# or `null` if there is none.
	fun attribute_decl(element_name: String,
			attribute_name: String,
			attribute_type: String,
			mode: nullable String,
			value: nullable String) do end