+Inside a fragment, the construct @code{%reldir%} is replaced with the
+directory of the fragment relative to the base @file{Makefile.am}.
+Similarly, @code{%canon_reldir%} is replaced with the canonicalized
+(@pxref{Canonicalization}) form of @code{%reldir%}. As a convenience,
+@code{%D%} is a synonym for @code{%reldir%}, and @code{%C%}
+is a synonym for @code{%canon_reldir%}.
+
+A special feature is that if the fragment is in the same directory as
+the base @file{Makefile.am} (i.e., @code{%reldir%} is @code{.}), then
+@code{%reldir%} and @code{%canon_reldir%} will expand to the empty
+string as well as eat, if present, a following slash or underscore
+respectively.
+
+Thus, a makefile fragment might look like this:
+
+@example
+bin_PROGRAMS += %reldir%/mumble
+%canon_reldir%_mumble_SOURCES = %reldir%/one.c
+@end example
+