Description:
------------
https://github.com/php/php-src/pull/2606 introduced two new constants
JSON_INVALID_UTF8_IGNORE and JSON_INVALID_UTF8_SUBSTITUTE
for the json_decode() and json_encode() functions
in PHP 7.2.0.

They are only briefly mentioned in the "PHP 7 ChangeLog" https://www.php.net/ChangeLog-7.php
and listed (without links) on the "Migrating from PHP 7.1.x to PHP 7.2.x" "New global constants" page https://www.php.net/manual/en/migration72.constants.php

But there is no mention of them in the reference pages:

 * https://www.php.net/manual/en/json.constants.php
 * https://www.php.net/manual/en/function.json-decode.php
 * https://www.php.net/manual/en/function.json-encode.php

(whereas there is for the JSON_THROW_ON_ERROR constant introduced later in PHP 7.3.0)