+
+&,lc => $(top_srcdir)/sub/dir/lc
+&,/ => $(top_srcdir)/sub/dir/
+
+&;lc => $(top_srcdir)/sub/dir/lc
+&;/ => $(top_srcdir)/sub/dir/
+
+&@lc => $(PWD)/sub/dir/lc
+&@/ => $(PWD)/sub/dir/
+
+&.lc => $(PWD)/lc
+&./ => $(PWD)/
+
+&@,lc => $(abs_top_srcdir)/sub/dir/lc
+&@,/ => $(abs_top_srcdir)/sub/dir/
+
+&@;lc => $(abs_top_srcdir)/sub/dir/lc
+&@;/ => $(abs_top_srcdir)/sub/dir/
+
+In general:
+ = return subdir without delimiter (not allowed with `,' `;' `@')
+ , pathname of this subdirectory in source tree
+ ; pathname of top level of source tree
+ . pathname of this directory in build tree, implies absolute pathnames
+ @ absolute pathnames (forbidden with `.', must come first)
+
+So pathname syntax is a subset of:
+ '&' [ '@' ] [ ',' | ';' | '.' ] [ lc | '/' ]
+
+ To avoid incomprehensible .sd.mk files, some combinations are not
+ allowed. For example `&@=./' would mean `$(PWD)/sub/dir' but can
+ be spelled `$(PWD)/&=/', but more normally the trailing / can be
+ tolerated, so use `&@/'.