Update targetRef according to API

`targetRef` is currently used differently than other API objects, it does not follow specification. Instead of `dataclass` we extend objects with `Referencable` which implements a method that extracts all necessary information to satisfy API. This approach is not wrong but differs from what we are used to. With the new implementation of `section_names` this needs to be investigated again.

Locate the targetRef implementation and the Referencable objects, then compare their behavior with the API specification. Investigate how the new section_names implementation affects the extracted information; the work is done when targetRef follows the API convention and its behavior is verified.

Written by the indexing model from the issue text.