s can arise when applications rely too much on extension types
        that are not recognized by other implementations. Care should be taken
        to not unduly overlap with or duplicate the existing Activity types.
      </p>
      <p>
        When an implementation uses an extension type that overlaps with a core
        vocabulary type, the implementation MUST also specify the core
        vocabulary type. For instance, some vocabularies (e.g. Schema.org)
        define their own types for describing 