Equivalent to Oracle's inline CURSOR in a SELECT clause?

In Oracle I can do this:

SELECT h.transaction_number
CURSOR(SELECT d.detail_number
FROM detail d
WHERE d.transaction_number=h.transaction_number)
FROM header h
WHERE h.transaction_date='25-aug-2004'

which comes in handy once in a while for nested parent/child
relationships, especially when using Oracle's XSQL servlet to produce
XML from queries.

Is there an equivalent syntax in PostgreSQL?

P.S. Half surprisingly, the Oracle XSQL servlet works just fine with
PostgreSQL as a backend!