The HTML vs XHTML situation: would you prefer a hard failure on any error, or a graceful degradation system that is therefore always slightly degraded?
We go back and forth on this because tightening the schema only works when you can adequately define the requirements of both ends up front, and there isn't a vendor battleground happening in your standard. Developers end up escaping into an unstructured-but-working zone. Classics like "it's such a hassle to get the DBA to add columns, so we'll add a single text column and keep all the data in there as JSON".
> tightening the schema only works when you can adequately define the requirements of both ends up front
There are degrees of tightening though, aren't there? It would be a matter of necessity (to me, at least) that an interface like he describes be extensible. To me, it's about better OS primitives with more guarantees, etc. Versioned APIs with options to fallback to older versions (to at least some extent) seems like an obvious outcome. The last thing anyone would want would be the equivalent of JSON in a database column, which would completely defeat the purpose.
> The HTML vs XHTML situation: would you prefer a hard failure on any error, or a graceful degradation system that is therefore always slightly degraded?
Definitely would prefer the hard failure. The community will literally fix all of that in a week -- all template engines and DOM generators will adapt to avoid the hard errors and everything has a good shot at becoming better as a result.
We go back and forth on this because tightening the schema only works when you can adequately define the requirements of both ends up front, and there isn't a vendor battleground happening in your standard. Developers end up escaping into an unstructured-but-working zone. Classics like "it's such a hassle to get the DBA to add columns, so we'll add a single text column and keep all the data in there as JSON".