Pull Request resolves #46610

• 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

Added a <base> tag to the Cassiopeia error.php template header. This ensures that relative assets (like images in custom modules) load correctly when a 404 error occurs on a nested URL.

Testing Instructions

Go to Administrator > Content > Site Modules
Create a "Custom" module
Set the position to error-404 and assign it to "All Pages"
In the content editor, switch to code view and add an image with a relative path:
for eg: <img src="images/powered_by.png" alt="Test Logo">
Visit http://yourdomain.com/thispagedoesnotexist -> the custom page appears correctly and the image is also visible.
Visit http://yourdomain.com/category/thispagedoesnotexist -> the custom error page does not load the image.

Actual result BEFORE applying this Pull Request

The image fails to load , and the "Home pagee" button links to a non-existent path.

Expected result AFTER applying this Pull Request

The image loads correctly, and the Home button correctly links to the site root.

Link to documentations

Please select:

• 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