[HACKERS] INSERT INTO arr2(array[1].d, array[2].d)

Over in [1], I was very surprised to discover $SUBJECT[2]. I looked in 
the docs, and they clearly indicate that INSERT accepts "column names".

What's the best way to describe this? "column expression"? "field 
expression"?

1: 
https://www.postgresql.org/message-id/20170311005810.kuccp7t5t5jhe736@alap3.anarazel.de

2:
CREATE TABLE arr(d int[]);
CREATE TABLE arr2(arr arr)
INSERT INTO arr2(arr[1].d, arr[2].d) VALUES(ARRAY[1,2],ARRAY[3,4]) 
RETURNING *
┌───────────────────────────────┐
│              arr              │
├───────────────────────────────┤
│ {"(\"{1,2}\")","(\"{3,4}\")"} │
└───────────────────────────────┘
-- 
Jim Nasby, Chief Data Architect, OpenSCG
http://OpenSCG.com