NotImplementedWarning: cannot process plain `owl:AnnotationProperty` cls(self).parse_from(_handle) # type: ignore

Firstly, thank you very much for this amazing library to manage ontologies!. I have been testing it for a couple of weeks, using the ChEBI ontology in two representations: [OBO](http://ftp.ebi.ac.uk/pub/databases/chebi/ontology/chebi_core.obo.gz) and [OWL](http://ftp.ebi.ac.uk/pub/databases/chebi/ontology/chebi.owl.gz) and all looks going well. However, I have a doubt regarding a warning that I got using OWL representation.

When the library loads the ontology, I get

```NotImplementedWarning: cannot process plain `owl:AnnotationProperty` cls(self).parse_from(_handle) # type: ignore```

So, I would like to understand why the warning appears only for OWL. I am not an expert in ontologies and I want to be sure that the library is not skipping details or important information.

Thank you.