JSONExp is a powerful, declarative method for matching structured data. Think of it as RegExps for JSON.
It is particularly useful not directly in code, but when it is desirable to give tech-savvy users a means of expressing patterns to be matched.
Aside: JSONExp is a key component in LiterAPI, a literate API testing framework. By making documentation written in Markdown executable, API developers can kill two birds with one stone: write documentation that's easy for an implementer to follow by being structured as explicit stories, and also have a way of testing that the API can faithfully execute the story.
JSONExps focus on the structure of the data, rather than the method used for matching it.