PG Bug reporting form <noreply@postgresql.org> writes:
> After upgrading postgresql from 9 to 12 the following statement no longer
> produces the same result: SELECT xpath('name()', '<abc>xyz</abc>'::XML)
> PostgreSQL 9 returns '{abc}'
> PostgreSQL 12 returns '{""}'
> This behavior changed in version 11 and perpetuated into 12.
This looks to me to be an intentional change in xpath's behavior.
The v11 release notes call out the incompatibility:
Correctly handle relative path expressions in xmltable(), xpath(), and
other XML-handling functions (Markus Winand)
Per the SQL standard, relative paths start from the document node of
the XML input document, not the root node as these functions
previously did.
Perhaps 'name(/*)' would do what you want now.
regards, tom lane