Xonotic makes usage of in-PK3 symbolic link to deduplicate files in distributed game, it’s a feature implemented in Darkplaces engine. This feature is also supported by the Dæmon engine.
NetRadiant level editor and q3map2 map compiler now supports them. This was one of the things preventing to edit map against released Xonotic assets. The other missing thing required to ditch the Xonotic mapping package is the support of the dds/ prefix, that will be addressed later.
The in-package symbolic link feature is supported in all zip-based packages including PK3, PK4 and DPK.
The support is minimal but good enough for the need: it only supports symbolic links within the same package and simple relative paths (for example: ../../textures/castle/brick.png).
It’s possible some textures look different in editor than with old mapping support package, it’s usually because of bugs in old mapping support package.