I believe the "box" type description is slightly incorrect:
# \dT box
Liste der Datentypen
Schema │ Name │ Beschreibung
────────────┼──────┼──────────────────────────────────────────
pg_catalog │ box │ geometric box '(lower left,upper right)'
While the syntax '((3,4),(1,2))'::box works, the canonical spelling is
'(3,4),(1,2)' and hence the description should be:
geometric box '(lower left),(upper right)'
Christoph