New wording from David G. Johnston, who noticed the unreadable original
also.  Include his suggested test case as well.

Fix a typo I noticed elsewhere while doing this.

Discussion: https://postgr.es/m/CAKFQuwY4Ld7ecxL_KAmaxwt0FUu5VcPPN2L4dh+3BeYbrdBa5g@mail.gmail.com