e16 is a quilt style package. For details on using quilt, see
/usr/share/doc/quilt/README.source.

The e16 package also uses a copy source scheme provided by
debian/builddir.mk. The top level directory files and sub-directories
(except for .pc/ and debian/) are copied to debian/build/ and the real
debian/ sub-directory is linked there. The patch, build, and install
targets are run in debian/build/. The unpatch target is not used.