Add tags to the fields of files.
The basic structure of the admin panel.
Get config files ready before entering the admin panel.
Include the Bootstrap from BootstrapCDN.
Add a subject to the model.
Work on the view.
Add fields to the configs.
Load data from files.
Add the action of save.
Validate the data on server side.
Save data.
Clean up.

- DRY: the `patt_tag' function extracts the tag matching pattern.
- Enhance error messages.
- Change the variable name `$obj' to `$config' for better meaning.
Extend the Config class and finish the ConfigAR class.
Extend the Config class and finish the ConfigRB class.
Clean up.

- DRY: the `my' prefix functions.
- Clean up error messages.