Use case:
Someone downloads a page from your website and stores it locally. Then the user opens it and the user will be tracked and the URL might look like
file:///C:/Users/myname/AppData/Local/...
This way we actually track personal data potentially by accident without knowing.
As this could be seen as a BC break we need to maybe wait for Matomo 5 for this and/or clearly announce this and warn users of this change.
see https://developer.matomo.org/guides/jstracker-core this would need to be changed in js/piwik.js
see how to embed tracking code https://developer.matomo.org/guides/tracking-javascript-guide