Surprising results from array concatenation

The docs (section 9.18 for PG 9.6) show as an example for array
concatenation

ARRAY[4,5,6] || 7

which works fine. However, trying the same with an array of text doesn't
work:

# select array['a','b','c'] || 'd';
ERROR: malformed array literal: "d"
LINE 1: select array['a','b','c'] || 'd';
^
DETAIL: Array value must start with "{" or dimension information.

Casting the second value to TEXT works.

# select array['a','b','c'] || 'd'::TEXT;
?column?
-----------
{a,b,c,d}
(1 row)

The assumption that the second argument is an array constant seems
surprising.

__________________________________________________________________________________
*Mike Blackwell | Technical Analyst, Distribution Services/Rollout
Management | RRD*
1750 Wallace Ave | St Charles, IL 60174-3401
Office: 630.313.7818
Mike(dot)Blackwell(at)rrd(dot)com
http://www.rrdonnelley.com

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* <Mike(dot)Blackwell(at)rrd(dot)com>*