The type of file to return the filename for, when used with.
These two options correspond rather directly to the 'dist' and 'built' terminology that automake uses and are explicitly used to distinguish between the 'srcdir' and 'builddir' being separate. All files in your project should either be dist (in the `DIST_EXTRA` or `dist_schema_DATA` sense, in which case they will always be in the srcdir) or built (in the `BUILT_SOURCES` sense, in which case they will always be in the builddir).
Note: as a general rule of automake, files that are generated only as part of the build-from-git process (but then are distributed with the tarball) always go in srcdir (even if doing a srcdir != builddir build from git) and are considered as distributed files.
a file that was included in the distribution tarball
a file that was built on the compiling machine