Should we recommend/require products to keep unknown extensions?

[tychonievich]

The current specification leaves undefined what an application may/should do when it encounters an extension tag that it does not fully support.

Should we require such to be kept? Recommend it? Recommend against it if the tool cannot show the data to users and let them edit it? Leave it unspecified?

[tychonievich]

Steering committee discussed 2021-12-14. The following points were raised:

• If an application uses a fixed database schema, then storing arbitrary extension tags is not readily achievable.
• If an extension overlaps semantics with a standard tag (perhaps its superstructure), then they need to be kept in sync if the extension tag is kept.
• If data is dropped, it is gone; if you don't then it is still there, but may no longer be accurate.
• Having data that the user does not see is not ideal. If it is all shown, then keeping it is useful, but many users may have trouble editing data that is shown but not integrated into the application.

For these reasons, we decided not to recommend keeping unknown extensions in general.