There exists a peculiar amnesia in software engineering regarding XML. Mention it in most circles and you will receive knowing smiles, dismissive waves, the sort of patronizing acknowledgment reserved for technologies deemed passé. “Oh, XML,” they say, as if the very syllables carry the weight of obsolescence. “We use JSON now. Much cleaner.”


That’s correct, but the order of tags in XML is not meaningful, and if you parse then write that, it can change order according to the spec. Hence, what you put would be something like the following if it was intended to represent an array.
<items> <item index="1"></item> <item index="2"></item> <item index="3"></item> </items>https://www.w3.org/TR/2004/REC-xml-infoset-20040204/
Does this not cover it?
Do you mean if you were to follow XML standard but not XML information set standard?
Information set isn’t a description of XML documents, but a description of what you have that you can write to XML, or what you’d get when you parse XML.
This is the key part from the document you linked
This is also a great example of the complexity of the XML specifications. Most people do not fully understand them, which is a negative aspect for a tool.
As an aside, you can have an enforced order in XML, but you have to also use XSD so you can specify xsd:sequence, which adds complexity and precludes ordered arrays in arbitrary documents.