**Summary**: Roolio is a lightweight JavaScript library that lets you build composable rule‑matching engines—craft sequences of “matchers” to test whether data satisfies specific criteria, either matching any rule (`match`) or all rules (`matchAll`). It’s ideal for developers who need expressive, reusable validation or routing logic in front‑end or Node.js applications, especially when they want to define custom matching rules without pulling in a heavyweight framework.