Worked on the metatensor/metatensor repository to improve the accuracy of the C API documentation, specifically addressing the semantics of the mts_labels_union function. Identified and corrected a documentation error where the function was described as performing a union, when it actually computes the intersection of two label sets. This update aligned the documentation with the actual C API behavior, reducing the risk of developer confusion and misuse. The work involved careful review and precise editing of technical documentation, leveraging skills in C API design and documentation practices, with additional experience in C++ and Rust contributing to a clear and maintainable API reference.