The following bug has been logged on the website:
Bug reference: 15426
Logged by: Ivan Ustûžanin
Email address: profic(at)gmail(dot)com
PostgreSQL version: 10.5
Operating system: Any
Description:
Executing
SELECT * FROM xmltable(
'.' PASSING '<r/>'
COLUMNS
c1 Text PATH 'name()',
c2 Text DEFAULT c1
);
complains that column c1 does not exist.
However the documentation states that it is possible to use prior columns in
default expressions of later columns.