Deprecate inheriting CSS classes in nested elements

[aschempp]

The ContentElementReference has a special attribute classes, which is then forwarded to the content element. The same should apply when rendering a regular content element from a reference (e.g. for nested elements).

The class is added to the template by all legacy elements: https://github.com/contao/contao/blob/5.x/core-bundle/contao/elements/ContentElement.php#L260

[m-vo]

Out of interest: where is this needed/in use?

[aschempp]

I have an element with nested fragments, and some of those fragments are legacy classes. If I remember correctly, the core uses the classes property to forward content element classes to a module fragment. In my case, I'm manually adding classes to the fragment reference (also see madeyourday/contao-rocksolid-custom-elements#169).

[leofeyer]

Thank you @aschempp.