<http://trac.webkit.org/changeset/106274> added a new CompositeOperator called CompositeDifference. In CoreGraphics, this maps to kCGBlendModeDifference (see <http://developer.apple.com/library/mac/#documentation/GraphicsImaging/Reference/CGContext/Reference/reference.html#//apple_ref/c/tdef/CGBlendMode>).
Closing this bug because the EFL port has been removed from trunk. If you feel this bug applies to a different upstream WebKit port and was closed in error, please either update the title and reopen the bug, or leave a comment to request this.