Worked on stabilizing the RNTupleWriter API within the root-project/roottest repository by migrating it from the ROOT::Experimental namespace to the top-level ROOT namespace. This refactoring effort focused on unifying the public API surface, updating all relevant examples to use ROOT::RNTupleWriter, and removing the experimental using declaration. By consolidating the API under the standard namespace, the changes improved consistency and reduced the risk of breaking changes for downstream users. The work was implemented in C++ and emphasized API design and careful refactoring, resulting in a more discoverable and maintainable interface for developers relying on the RNTupleWriter functionality.