+Adding `@' means "absolute path". This is not needed with &. because
+there is never any need to use &. since it would expand to nothing.
+`/' terminates the escape (needed if the next thing is not a lowercase
+character, or space). `=' means "just the value, no /". Space starts
+multi-word processing.
+
+ Recommended In build tree In source tree
+ when Relative Absolute Relative Absolute
+
+ 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
+ level any file &./file &;/file &@;/file
+ several f g h &. f g h &; f g h &@; f g h
+ .mk.in file $(abs)/file $(src)/file $(abs_src)/file