Plugins case study: mdBook preprocessors

mdBook, a popular Rust documentation tool, implements a flexible preprocessor plugin system that allows arbitrary programs to modify book content before rendering. The mechanism uses JSON-based inter-process communication, enabling plugins in any language while providing enhanced API support for Rust implementations. The architecture demonstrates fundamental plugin concepts including explicit discovery through configuration, dual-invocation registration, coarse-grained hooks passing entire book contents, and language-specific API exposure. A similar renderer/backend plugin system handles final output generation.