+Tables of file reference syntaxes
+---------------------------------
+
+In a nonrecursive makefile supporting out of tree builds there are
+three separate important distinctions between different file
+locations:
+
+ (i) In the build tree, or in the source tree ?
+
+ (ii) In (or relative to) the subdirectory to which this Subdir.sd.mk
+ relates, or relative to the project's top level ?
+
+ (iii) Absolute or relative pathname ?
+ (Usually relative pathnames suffice.)
+
+Path construction &-expansions are built from the following:
+
+ Relative paths in... Absolute paths in...
+ build source build source
+
+ This directory & &, &@ &@,
+ Top level . &; &@. &@;
+
+In more detail, with the various options for what comes next:
+
+ Recommended Relative paths in... Absolute paths in...
+ for build source build source
+
+ This lc &file &,file &@file &@,file
+ directory any &/file &,/file &@/file &@,/file
+ several & f g h &, f g h &@ f g h &@, f g h
+
+ Top lc file &;file &@.file &@;file
+ level any file &;/file &@./file &@;/file
+ several f g h &; f g h &@. f g h &@; f g h
+ .mk.in file $(src)/file $(abs)/file $(abs_src)/file
+