# Look up an attribute's value 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.
	#
	# See `value_of` for a description
	# of the possible values.
	#
	# Parameters:
	#
	# * `uri`: Namespace URI, or the empty string if
	# the name has no Namespace URI.
	#
	# * `local_name`: attribute's local name.
	#
	# Returns:
	#
	# The attribute value as a string, or `null` if the
	# attribute is not in the list or if Namespace
	# processing is not being performed.
	redef fun value_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 data[i + 4]
				end
				i += 5
			end
		end
		return null
	end