[postgis-users] exterior rings in multipolygons

[Mr. Puneet Kishor]

Please help me understand the following

====
SELECT 
    ST_Nrings(the_geom) nr, 
    ST_NumInteriorRings(the_geom) nir, 
    ST_AsText(the_geom) WKT 
FROM table 
WHERE objectid = 280;

nr  nir  WKT
--  ---  ----------------------------------------------------------------
 4    3  "MULTIPOLYGON(((..),(..),(..),(..)))"

====

Looking at the above, I am assuming the first (..) is the exterior ring, and the remaning three (..) are the 3 interior rings. However,

====
SELECT ST_ExteriorRing(the_geom) er  
FROM table 
WHERE objectid = 280;

ERROR: ExteriorRing: geom is not a polygon
====


So, what is going on? Of course, the docs say that ST_ExteriorRing doesn't work on a MULTIPOLYGON. So, is the above only an implementation anomaly, and I can treat the first ring as an exterior ring? Or, is it really something else?