Coverage of config parameter/value storage for app and core developers

I think this would be some useful information to compile for app as well as core developers.

Not just solely for documentation purposes, but from a systems design perspective.

Potential content coverage (eventually, not necessarily initially):

• When to use each type (other than user):
  • config/config.php
    • i.e. when required for (during) initial installation (but not post-install configuration matters); when required to be available to the built-in Updater
  • system config values
  • system core config values
  • app config values
  • user-level values (i.e. specific to admins)
• Special policies (if any)
  • re: config/config.php
    • i.e. usage by non-shipped apps
  • Exceptions
    • Grandfathering (For Now)
    • Grandfathering (For Reasons)
• How-to:
  • Document
  • Deprecate
  • Migrate

That said, currently I'd probably label this:

• nice to have
• future tech debt

So still probably low priority (unless someone just finds themselves really compelled to jump on it of course).

Start by inventorying the configuration locations named in the issue, including config/config.php, system config values, system core config values, app config values, and user-level values. Define the intended documentation scope for usage, special policies, exceptions, and how to document, deprecate, and migrate settings. Done means these choices and procedures are clearly documented for app and core developers.