Config Presets
Config presets are simply copies of the config file at a certain state, saved in YAML format without comments (to save space) in a config-presets folder under the directory where configs are saved (either config or serverconfig). The values inside these preset files can be read and easily applied to the config file at any moment.
As they're paired with a config file, presets can only cover entries from a single file.
While you could manually manage these preset files, Simple Config allows you to easily save the currently edited values as a preset file at any moment.
Simple Config menus have a dedicated toolbar in the top right corner to manage presets for the current config file. Keep in mind that every config type accessible in the same menu represents a different config file, and as such, presets can only cover one type each.
This is represented by the icons displayed in the preset toolbar, which identify presets with their types and save location. You won't be able to select presets from a different type than the one you're currently editing.
Presets can be saved locally or remotely in a multiplayer server. To save presets in a server, you must be connected to one, and have been granted permissions to save presets in the server (see Config Permissions).
All players connected to the server will be able to use presets saved in the server, so this is a great way to provide players of a server you manage a bunch of default settings they can use.
Additionally, resource packs/mods can also provide default/built-in read-only presets to help make mods easier to setup initially (see Built-in Presets and Hotkeys).
When a config preset is applied, its entries are read and written over the currently edited ones.
This means, if a config preset doesn't define all of the entries in a config file, it will only affect the ones it contains.
To achieve this, you don't need to manually erase entries inside preset files, as Simple Config allows you to select entries from the menu before saving a preset. If you save a preset with some entries selected, it will only save those entries in the preset. The dialog that appears to confirm saving a preset will inform you of how many entries will be saved.
You can use this feature to create patches to quickly change a group of related settings, without worrying about all the others.
Likewise, when applying a preset, if you have some entries selected, the preset will only be applied to the entries you have selected.