Dev:WorkflowKit.framework

WorkflowKit is the framework that acts as a backend to the Shortcuts app. It provides around 80% functionality of the Shortcuts app including (but not limited to) actions (though ActionKit also powers a lot of them), handles how shortcuts are imported, how they're stored, etc. It is noted that while it is technically added in 12.0, most of its functionality came in iOS 13.0.

For examples on how to use this framework, see the Example Code section of this page.

WFWorkflowRecord
WFWorkflowRecord is how shortcuts are stored. The biggest thing is actions: Every action has an action identifier to identify an action (WFWorkflowActionIdentifier), and some have parameters of what is in said action (WFWorkflowActionParameters). However, it also handles other data about the shortcut, such as its name and minimum client version it can be imported on.

WFBundledActionProvider
WFBundledActionProvider is what provides WorkflowKit with what actions it loads.

WFAction
WFAction is basically the class that every shortcuts action uses. It should be noted that actions aren't all WFAction, but rather their own class that inherit from it (For example, WFExitShortcut in ActionKit).