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> But I've never once seen an application that will actually preserve that property.

I wonder if author uses Chrome, which depends heavily on this in its Sync feature.

Yeah, most big Google services -- including Search -- rely pretty heavily on unknown field retention. Google has been building large services out of microservices since a decade before anyone ever said the word "microservice". When one service is updated to emit a new field, and another service is updated to consume it, it's important that the feature can then work, without updating all the middlemen.

When I worked on Chrome Sync, we spent some time making sure that unknown fields were preserved properly. Glad to see that someone noticed, cheers!

I did notice that when I was an owner of protobuf in Chromium :) Custom patches to support unknown field preservation in lite mode sure brought me some hassle when updating to version 3 of the library.

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