+`the current directory'. There are a variety of convenient
+constructions.
+
+The result is that to a large extent, the Subdir.mk.in has an easy way
+to namespace its "local" make variables, and an easy way to refer to
+its "local" filenames.
+
+The Subdir.mk.in's are filtered, fed through autoconf in the usual way
+(for @..@-substitutions) and included by one autogenerated toplevel
+makefile.
+
+So all of the input is combined and passed to one make invocation. (A
+corollary is that there is no enforcement of the namespacing:
+discipline is required to prefix relevant variable names with &, etc.
+
+Each subdirectory is also provided with an autogenerated `Makefile'
+which exists purely to capture ordinary make invocations and arrange
+for something suitable to happen.
+
+Where there are dependencies between subdirectories, each Subdir.mk.in
+can simply refer to files in other subdirectories directly.
+
+Per-directory targets, "recursion"
+----------------------------------
+
+Each subdirectory has its own `all' target. For example a
+subdirectory `src' has a target `src/all'. The rules for these are
+automatically generated from the settings of the per-directory
+&TARGETS variables. (In src/Subdir.mk.in, this of course refers to a
+make variable called src_TARGETS.)
+
+The `all' target in a parent directory is taken to imply the `all'
+targets in all of its subdirectories, recursively. And in the
+autogenerated stub Makefiles, `all' is the default target. So if you
+just type `make' in the toplevel, you are asking for `&all'
+(<subdir>/all) for every directory in the project.
+
+In a parallel build, the rules for all these various subdirectory
+targets may be in run in parallel: there is only one `make'
+invocation at a time.
+
+There may also be other
+
+
+
+
+
+
+ (None of this prevents