@RichardWallis I'm not super happy with this change to the core, which snuck through as part of a pending proposal for touristy stuff. It is entirely reasonable to want to relate trips in this way, but we should not have made a core change to the (currently 100% CreativeWork-centric) isPartOf property as part of the tourism proposal. My bad for not catching this earlier.

      <span class="h" property="rdfs:label">hasPart</span>
      <span>Domain: <a property="http://schema.org/domainIncludes" href="proxy.php?url=http://schema.org/Trip">Trip</a></span>
      <span>rangeIncludes: <a property="http://schema.org/rangeIncludes" href="proxy.php?url=http://schema.org/Trip">Trip</a></span>
      <span>Category: <span property="schema:category">issue-1810</span></span>
    </div>
    <div typeof="rdf:Property" resource="http://schema.org/isPartOf">
      <span class="h" property="rdfs:label">isPartOf</span>
      <span>Domain: <a property="http://schema.org/domainIncludes" href="proxy.php?url=http://schema.org/Trip">Trip</a></span>
      <span>rangeIncludes: <a property="http://schema.org/rangeIncludes" href="proxy.php?url=http://schema.org/Trip">Trip</a></span>
      <span>Category: <span property="schema:category">issue-1810</span></span>
    </div>

This looks like a bug to me. Many times we've had this discussion and there has never been consensus in the community or steering group to generalize isPartOf to other entity types. At this point I always point at https://plato.stanford.edu/entries/mereology/ and say "do we really want to go there"? I continue to believe we don't want to go there.

@rvguha can you give some KR oversight here please. The desire is for our existing Trip type to have a pattern for trips being parts of trips.

I believe we have prior consensus

From #1097 (comment) in 2016,

Richard: At first glance the basic proposal of having Thing in the range of isPartOf
that raises a +1 from me.
Vicki: Do we have a use case for this change? I hesitate to make such a large change without a compelling use case.
Dan:
My proposal would be to define dedicated properties for specific use cases e.g. for food we might have containsChemical, for places we already have containsPlace, for people who are "part of" organizations we have already got "affiliation", and for sub-events within a larger/longer containing event, we already have subEvent.
Guha: I tend to agree with Vicki and Dan. I would really like to avoid going down the path of making Thing the domain and range of too many properties.

The question to me seems to be - do we handle trips via Event, or do they have a good reason to be handled separately as an Intangible. There have been reasonable questions asked on the mailing list about this recently too.