Saxon

Order of attributes has always been undefined / implementation-defined, though many XML parsers retain the original attribute order and many operations in Saxon do so. We have made changes in 10.0 to allow finding an attribute in a large collection of attributes more efficient; this uses a HashMap which does not retain order.

There's no guaranteed way of keeping the original attribute order, but you can control the attribute order in the serialized result using the saxon:attribute-order output parameter. (Needs PE or higher).

You could try tweaking the static variable net.sf.saxon.om.SmallAttributeMap.LIMIT, currently set to 5, to a higher number; this is the threshold for using the large attribute set implementation. You would have to change the source code or use reflection because the variable isn't public.

Thank you for your answer. But somehow the order has to be present because @*/. gives the attributes in "document order", right?

There's a stable order of attributes, but it's not predictable, and it's not necessarily related to the lexical order of attributes in the serialized XML.

It was a bit strange to see that the order of the attributes in the result tree no longer determines the order in the serialized XML, but it may also be a mind switch. And of course we prefer a better performance over a more human readable result. We will probably use saxon:attribute-order = "*" as a compromise from now on. Our customers will detect a large number of differences once (based on a digest calculation), but after that everything will remain stable. Thank you for the explanation.