…t and improve documentation

* Moved inner function `functionName` outside its parent function for better code organization and readability.
* Improved JSDoc annotations for `functionName`, detailing parameters, return type, and usage.

…better highlighting

* Changed `//` comments to `/** */` for comments that include `@example` annotations.
* Ensured proper JSDoc format so that code editors correctly highlight the examples.

… security against header spoofing

* Introduced a new `trustDownstreamProxy` option in the `options` object to control whether `X-Forwarded-XXXX` headers should be considered.
* This boolean option defaults to `true` to maintain backward compatibility while enhancing security.
* When set to `false`, the `X-Forwarded` headers are ignored, reducing the risk of header spoofing.