Custom Widget API's will generate documentation, but what about the private widget api?

Good question.

"Private" APIs exposed to widgets in IScriptablePlugins are indeed auto-documented within Widget Studio's documentation panel and autocomplete suggestions when viewed from within the associated plugin's widgets, the same as the platform's public APIs, and they'll even be identified with a "private" tag.

The only "gotcha" is to ensure that the custom api object exposed via IContextualScriptedContentFragmentExtension.GetExtension(NameValueCollection) should be able to return an object instance even with a null or empty NameValueCollection passed to GetExtension(). The resulting object, even if unusable in that state, is reflected upon to know the documentable private API details.

Good question.

"Private" APIs exposed to widgets in IScriptablePlugins are indeed auto-documented within Widget Studio's documentation panel and autocomplete suggestions when viewed from within the associated plugin's widgets, the same as the platform's public APIs, and they'll even be identified with a "private" tag.

The only "gotcha" is to ensure that the custom api object exposed via IContextualScriptedContentFragmentExtension.GetExtension(NameValueCollection) should be able to return an object instance even with a null or empty NameValueCollection passed to GetExtension(). The resulting object, even if unusable in that state, is reflected upon to know the documentable private API details.