ini setting zend.assertions should changeable PHP_INI_PERDIR without restriction

Description

Currently, if the ini setting zend.assertions is set to -1 in php.ini, it cannot be set to a different value in per-directory configuration file (PHP_INI_PERDIR) .user.ini or .htaccess (and vice versa).

I want to be able to change zend.assertions PHP_INI_PERDIR without restriction, for the following reasons:

1. I have not always write access to php.ini;
2. I don’t know the PHP_INI_PERDIR equivalent of
   <?php if (ini_get('zend.assertions) !== '-1') ini_set('zend.assertions', '1'); ?>
   in order to avoid an E_WARNING.

(Note that there is at least one other ini setting, namely short_open_tag, that also modify the result of compilation, but that is nevertheless changeable PHP_INI_PERDIR; from which I infer that my request is not unreasonable.)

The issue concerns zend.assertions in php.ini and per-directory .user.ini or .htaccess configuration; begin by tracing how these contexts handle that setting. Done means a value set in one context can be changed to another without the current restriction or resulting E_WARNING.