BUG #16770: PostgreSQL software V11 does not eliminate this recheck_on_update option?

The following bug has been logged on the website:

Bug reference: 16770
Logged by: yanliang lei
Email address: leiyanliang(at)highgo(dot)com
PostgreSQL version: 11.10
Operating system: CentOS7.6
Description:

in pg11 create index statement have recheck_on_update option，but this option
do not exist in the documents
in the pg11.1 releasenote，recheck_on_update optimization is
disabled(https://www.postgresql.org/docs/11/release-11-1.html)
and in the pg11 create index
document(https://www.postgresql.org/docs/current/sql-createindex.html#SQL-CREATEINDEX-STORAGE-PARAMETERS)，there
is nothing about recheck_on_update

but the create index sql with recheck_on_update='on' execute succuessfully,
why? PostgreSQL software V11 does not eliminate this recheck_on_update
option?

postgres=# CREATE INDEX idx1_t_tab_x ON t_tab_x(upper(c4)) WITH
(recheck_on_update = on) ;
CREATE INDEX
postgres=# \d+ t_tab_x
Table "public.t_tab_x"
Column | Type | Collation | Nullable | Default | Storage
| Stats target | Description
--------+-----------------------+-----------+----------+---------+----------+--------------+-------------
c1 | integer | | not null | | plain
| |
c2 | integer | | not null | | plain
| |
c3 | integer | | | | plain
| |
c4 | character varying(10) | | | | extended
| |
Indexes:
"t_tab_x_pkey" PRIMARY KEY, btree (c1, c2) INCLUDE (c3)
"idx1_t_tab_x" btree (upper(c4::text)) WITH (recheck_on_update='on')

postgres=# \d+ idx_t_tab_x
Did not find any relation named "idx_t_tab_x".
postgres=# \d+ idx1_t_tab_x
Index "public.idx1_t_tab_x"
Column | Type | Key? | Definition | Storage | Stats target
--------+------+------+-----------------+----------+--------------
upper | text | yes | upper(c4::text) | extended |
btree, for table "public.t_tab_x"
Options: recheck_on_update=on

postgres=#
postgres=# select version();
version

----------------------------------------------------------------------------------------------------------
PostgreSQL 11.10 on x86_64-pc-linux-gnu, compiled by gcc (GCC) 4.8.5
20150623 (Red Hat 4.8.5-39), 64-bit
(1 row)

postgres=#