Savepath of default (UI-) Assets

Unity Engine
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1

Hello guys,
does anyone knows where Unity saves the default assets on disk like ‘UISprite.psd’. There is the option to load the built in assets with

AssetDatabase.GetBuiltinExtraResource<Sprite> ("UI/Skin/UISprite.psd");

But i can not find these folders or files.
Thanks

2

These builtin assets are stored in asset bundles next to the Unity executable.