# Look up an attribute's type by index.
	#
	# The attribute type is one of the strings `CDATA`, `ID`,
	# `IDREF`, `IDREFS`, `NMTOKEN`, `NMTOKENS`, `ENTITY`, `ENTITIES`,
	# or `NOTATION` (always in upper case).
	#
	# If the parser has not read a declaration for the attribute,
	# or if the parser does not report attribute types, then it must
	# return the value `CDATA` as stated in the XML 1.0 Recommentation
	# (clause 3.3.3, "Attribute-Value Normalization").
	#
	# For an enumerated attribute that is not a notation, the
	# parser will report the type as `NMTOKEN`.
	#
	# Parameters:
	#
	# * `index: Int`: attribute index.
	# * `index: String`: XML 1.0 qualified (prefixed) name.
	# In many cases, it will be more efficient to look up the name once and
	# query by `Int` index rather than quering by name repeatedly.
	#
	# Returns:
	#
	# The attribute's type as a string, or `null` if the specified
	# attribute is not in the list or if qualified names
	# are not available.
	#
	# SEE: `length`
	redef fun type_of(index) do
		if index isa Int then
			if index >= 0 and index < length then
				return data[index * 5 + 3]
			end
		else if index isa String and "" != index then
			var i = 0

			while i < data.length do
				if data[i + 2] == index then
					return data[i + 3]
				end
				i += 5
			end
		end
		return null
	end