Decodal/doc/manual/source/language/expression/path-reference.md

Path Reference Expression

A path reference expression accesses a field of an object.

config.host
config.feature_hoge.enable

Evaluation

The expression on the left is evaluated as an object, then the named field is referenced. The referenced field is not evaluated until needed.

Referencing a field that does not exist produces a diagnostic. An explicit Unknown range does not represent a missing field, so it does not make field presence ambiguous.