Currently, includes are collected as much as any "real" definitions into the registries, e.g. for the mtk:components/linkSwitchableField dialog.

However, in the case above, the root definition is a FieldDefinition; it can be transformed by map2bean successfully, and will claim thus to be "valid", however, a #get() call on such provider will throw a ClassCastException, the resolved bean type being incompatible with the provider's generic type.

Considering all definitions should match the registry's declared type to be deemed valid—that's a step we don't have atm—this should apply to includes as well.
If we ever want to denote the included file is valid YAML, that's a different sense of validity, not that of the definition provider.