There are a number of site configuration options in Admin menu -> Configure site -> Site options that can be added to the config.php file and then not be changed by a site admin. These are not yet listed in config-defaults.php. That makes it harder to know which options set on the front-end could be added to the config.php file to prevent a site admin to unset them accidentally. Since it requires that code is read to find that out, it's rather cumbersome to achieve without trial and error.
From Robert: It's all the options that have $OVERRIDDEN as part of their markup and use get_config() to fetch their default value as get_config() uses the values in config.php over what is in the db and $OVERIDDEN just makes the filed disabled if using config.php value.
All of these options should be added to lib/config-defaults.php in their own section: Can be set in 'Site options' so it's clear that both ways are possible.
Only brief comments are necessary as the details are in the Mahara manual. The main comment could even be taken from the option's description line for the most part.
Patch for "master" branch: https:/