What is a key feature of JSON as a data format?

A key feature of JSON (JavaScript Object Notation) as a data format is the use of key-value pairs. This structure allows for easy representation and organization of data in a way that is both human-readable and machine-readable. Each key is a unique identifier within an object, and associated with it is a value that can be a string, number, array, object, or boolean. This format is efficient for data interchange, especially in web applications, because it is lightweight and easily parsed by JavaScript and other programming languages, supporting seamless data communication between a server and a client.

In contrast, the other options do not accurately describe JSON's fundamental characteristics. JSON is not XML compatible; while both are data interchange formats, they have distinct syntaxes and structures. JSON does not use a hierarchical structure with tag elements like XML; instead, it represents data using a simpler syntax based on key-value pairs and arrays. Lastly, JSON is primarily designed for text-based data representation and does not natively support binary data transfer as a standard feature, unlike some other formats such as Protocol Buffers or MessagePack. This clarity and simplicity make JSON a popular choice for APIs and web services.