Yes, you're just looking in the wrong place.
What you're looking at there is the documentation for validation callbacks into an Add-In, which is how you implement your own validation rules. The methods to execute a validation are in the Project class.
The Project is a singleton, accessed from the Repository class, which is also a singleton and which is available in the context of an executing script.
Note, however, that there are no API calls to select which validation rules are used; this can only be done via the GUI. Which makes the whole exercise a little frustrating.