On 01/24/25 14:59, Jim Jones wrote:
> In the XML Query standard, a "document node" represents a relaxed
> version of an XML document structure. This corresponds to what
> PostgreSQL's single XML type allows, meaning that any valid non-null
> PostgreSQL XML value can be returned unchanged. Other systems may
> support more permissive XML data types, such as
> <literal>XML(SEQUENCE)</literal>, which allow values that do not conform
> to this structure. In PostgreSQL, every valid non-null value of the XML
> type already has that structure, making any additional processing by
> this function unnecessary.
My one question here would be, does the reader of that paragraph
sit back and wonder "why have we suddenly begun talking about
the XML Query standard?".
It seems to me the key connection there is that the ISO SQL standard
defines XMLDOCUMENT by equivalence to what `document { $expr }` means
in the W3 XML Query standard.
Once that connection is made, it is all smooth sailing.
Regards,
-Chap
