XCF is the native file format for GIMP (GNU Image Manipulation Program). It supports all the possible information about an image, including layers and transparency, except for undo information.
- GIMP Brush (.gbr)
- GIMP Animated Brush (.gih)
- GIMP Gradient (.ggr)
- GIMP Pattern (.pat)
- GIMP Palette (.gpl)
The first 9 bytes of an XCF file are the ASCII string "
gimp xcf ".
The Wikipedia article says that the reference documentation is the source code for GIMP itself.