Property format.name is now protected

Does that mean we need some test coverage for that? this is pretty tricky :)

Do you maybe know whether we can ask twig to fail in case something like this happens and not just silently ignore it? (I guess this is what is happening).

We should be able to test this easily be checking for that markup on a page that prints this. We did find this because of w3c html validation, in fact ;)

I don't know how to do tell twig when to report and error and when not?

+++ b/core/modules/filter/src/Tests/TextFormatElementFormTest.php
@@ -117,6 +117,10 @@ public function testTextFormatElement() {
+    $this->assertNoPattern('|<h4[^>]*></h4>|', 'Title in the H4 element is not found.');

Assertion message is a bit confusing, I'd suggest "No empty H4 element found".

Thanks, this looks good to me. As mentioned, I don't really see how we could change anything in regards to how twig works.. that it doesn't give notices/errors is kind of a feature.

The only thing i can think of would be to given an explicit error if object.property not resolved into anything *and* it is a protected property. But that would also cost processing time.

Template changes are unfrozen in beta and this is fixing a bug. Committed c706fd7 and pushed to 8.0.x. Thanks!