/usr/lib/mime/packages/xcftools is in xcftools 1.0.7-5.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 | image/xcf; xcfview '%s'; priority=5
image/x-xcf; xcfview '%s'; priority=5
application/x-xcf; xcfview '%s'; priority=5
|