Note that they explicitly point out that this is a bad idea to use in your code:
As a general rule, relying on this will lead to brittle code. Which IDs end up mapping to this API can vary over time, as new features are added to the Web platform, for example. Instead of this, use document.getElementById() or document.querySelector().
For further actions, you may consider blocking this person and/or reporting abuse
We're a place where coders share, stay up-to-date and grow their careers.
This is specified the WHATWG spec, html.spec.whatwg.org/#named-access...
Note that they explicitly point out that this is a bad idea to use in your code: