Use JSDoc comments to annotate functions and types.

Be concise in JSDoc comments, and only provide JSDoc comments if the function's behaviour is not self-evident.

Use the JSDoc inline `@link` tag to link to other functions and types within the same file.

```ts
/**
 * Subtracts two numbers
 */
const subtract = (a: number, b: number) => a - b;

/**
 * Does the opposite to {@link subtract}
 */
const add = (a: number, b: number) => a + b;
```
