steps to reproduce

1. install Ibexa DXP v3/v4
2. Create custom style block and custom style inline (https://doc.ibexa.co/en/3.3/extending/extending_online_editor/#configure-custom-styles)
3. Create an article
4. use created custom styles, first custom style block and next into custom style use custom style inline
5. try to publish

Result

Showing error "Validation of XML content failed"

Expected

Validation should pass without errors