No separate issue is linked.

• I read the Generative AI policy and my contribution is either not created with the help of AI or is compatible with the policy and GNU/GPL 2 or later.

Summary of Changes

For URL fields allowing relative URLs, detect the current site's hostname followed by a valid boundary rather than comparing the whole input with the hostname. Prepend the protocol for host-plus-path/port/query inputs while retaining normal relative-path handling. Escape the hostname before matching and reject lookalike hostname prefixes.

Testing Instructions

Run php ./libraries/vendor/bin/phpunit --configuration phpunit.xml.dist --filter UrlFilterTest in a configured Joomla development checkout. The fixture uses host www.example.com and root /joomla. Check hostname-only, path, port, query, uppercase host, lookalike host, relative path, absolute path, and full URL cases. These are reproduction instructions, not a claim of a local test run in this update.

Actual result BEFORE applying this Pull Request

www.example.com/blog/post is treated as a relative path and prefixed with /joomla/.

Expected result AFTER applying this Pull Request

The result is http://www.example.com/blog/post. A different host such as www.example.com.evil.org/page remains a relative input; ordinary relative and full URLs keep their existing handling.

Link to documentations

• Documentation link for guide.joomla.org:

• No documentation changes for guide.joomla.org needed

• Pull Request link for manual.joomla.org:

• No documentation changes for manual.joomla.org needed

These changes restore preservation of existing URL components rather than introduce a new public API.