tl;dr: UHF X11 turns the Apple Vision Pro into a full X11 display server, rendering each top-level X client as its own rootless spatial window in visionOS. It accepts TCP connections from external X clients with MIT-MAGIC-COOKIE-1 authentication, supports custom bitmap fonts, and includes experimental indirect GLX for OpenGL apps. Retro flair comes via CRT scanlines, phosphor masks, glow, and vignette effects.