A wide-spectrum language (WSL) is a programming language designed to be simultaneously a low-level and a high-level language—possibly a non-executable specification language. Wide-spectrum languages are designed to support a programming methodology based on program refinement. The concept was introduced by F. L. Bauer et al. in 1978: The advantage of a single language rather than separate specification, high-level, and low-level languages is that the program can be incrementally refined, with intermediate versions retaining some higher-level and some lower-level constructs.