The standard specifies the 2compositeOp" XML tag for layers. However, the valid values and their meaning is not specified. The different valid values should be enumerated along with their definition (formula). How new values can be added should also be documented.
Fixed by http://create.freedesktop.org/w/index.php?title=OpenRaster%2FLayers_Stack_Specification&diff=15431&oldid=15377 Note that the attribute name was changed from compositeOp to composite-op. Implementations underway for GIMP, Krita and GEGL.
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