Why format() adds double quote?

test=# select format('%I', t) from t1;
format
----------
aaa
"AAA"
"あいう"
(3 rows)

Why is the text value of the third line needed to be double quoted?
(note that it is a multi byte character). Same thing can be said to
quote_ident().

We treat identifiers made of the multi byte characters without double
quotation (non delimited identifier) in other places.

test=# create table t2(あいう text);
CREATE TABLE
test=# insert into t2 values('aaa');
INSERT 0 1
test=# select あいう from t2;
あいう
--------
aaa
(1 row)

Best regards,
--
Tatsuo Ishii
SRA OSS, Inc. Japan
English: http://www.sraoss.co.jp/index_en.php
Japanese:http://www.sraoss.co.jp