Why those advanced features are not documented?

For using Rescript for several years, i gradually know that there are some features like GADT, local abstract type, module type constaint and others… are not documented in our offical documentation. The only way i could found how to use those features is that reading the OCaml books first, and then, use command rescript convert to converting the OCaml code into rescript. Is this because those features will be deprecated in Rescript in the future?