# Look up the index of an attribute by Namespace 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.
	#
	# Parameters:
	#
	# * `uri`: Namespace URI, or the empty string if
	# the name has no Namespace URI.
	# * `local_name`: attribute's local name.
	#
	# Returns:
	#
	# The index of the attribute, or -1 if it does not
	# appear in the list.
	redef fun index_ns(uri, local_name) do
		var i = 0

		if "" != local_name then
			while i < data.length do
				if data[i] == uri and data[i + 1] == local_name then
					return i / 5
				end
				i += 5
			end
		end
		return -1
	end