`Symbol` is the built-in function used to create symbol values. Call it without `new`: each call produces a unique value, even when two calls use the same description. Symbols make useful object-property keys when a name must not collide with an ordinary string key or another independently created symbol. section 7.2
A description is not an identity
`const a = Symbol('name'); const b = Symbol('name');` gives `a !== b`. An object can hold both `obj.name` and `obj[a]`; `obj[Symbol('name')]` does not retrieve the value stored at `obj[a]`. Keep the symbol reference if other code needs that property. section 7.2
Symbol keys are less visible to conventional property enumeration: `Object.keys` and `Object.getOwnPropertyNames` do not return them. They are not private, however. `Object.getOwnPropertySymbols` and `Reflect.ownKeys` can discover them. Ordinary object spread and `Object.assign` can also carry symbol-keyed properties into a copy, retaining the same symbol reference. Use symbols for collision-free contracts, not as a security boundary. section 7.2 section 7.4.1
Use `Symbol.for('version')` when separate parts of an application must agree on one key without sharing a local symbol variable. It looks up the key in the runtime-wide global symbol registry, creating the symbol if necessary; `Symbol.keyFor(symbol)` retrieves a registered symbol’s key. A symbol made with `Symbol('version')` is not registered, so `Symbol.keyFor` returns `undefined` for it. section 7.3.2
A versioned application contract
A block exposes `get [Symbol.for('version')]() { return VERSION; }`. Mining code reads `block[Symbol.for('version')]` and selects the corresponding proof-of-work module. The shared key avoids relying on an ordinary property name that might collide with other code. section 7.4.2
An opt-in serialization hook
An object can implement `[Symbol.for('toJson')]()` to return its tailored JSON representation. A shared `toJson` helper calls that method when present and otherwise falls back to `JSON.stringify(obj)`. This gives objects a serialization contract without claiming a common string-named method. section 7.4.3
Symbols also serve as static hooks for behavior associated with fundamental operations such as iteration, primitive conversion, and printing. Their broader role is interoperability: a stable, collision-free property key lets objects participate in a convention without adding another ordinary name to their interface. section 7.0 section 7.8
