Can I use both the “built-in” expectations and custom ones in the same Datasource?
Yes, you can. You implement custom expectations in a class that you create by extending one of the Great Expectations dataset classes. Then you use the name of this class as the value of “class_name” in the “data_asset_type” section of your Datasource configuration in the great_expectations.yml config file of your project. Your class has both the built-in expectations and the custom ones that you added.