X-Git-Url: https://www.chiark.greenend.org.uk/ucgi/~ian/git?p=subdirmk.git;a=blobdiff_plain;f=README;h=cfd7ad03d1853cc3b8e68b6847ee1df079d401ca;hp=c9e4c0f9234f2fe42bac8187dd98c88784bb417a;hb=c0b216c79763f720df20e002fc14c9348a0e05c2;hpb=0a6ac67828982aca4e3c8ac73669420a30c70f34

diff --git a/README b/README
index c9e4c0f..cfd7ad0 100644
--- a/README
+++ b/README
@@ -105,6 +105,19 @@ is already provided in subdirmk, for you to reference like this:
   &:include subdirmk/clean.sd.mk
 For example you could put that in Perdir.sd.mk.
 
+The top-level Subdir.sd.mk is the first makefile included after the
+autogenerated `main.mk' which merely has some basic settings and
+includes.  So if you want to get in early and set global variables,
+put them near the top of Subdir.sd.mk.
+
+subdirmk's filter script itself sets (only) these variables:
+  top_srcdir
+  abs_top_srcdir
+  SUBDIRMK_MAKEFILES
+  MAKEFILE_TEMPLATES
+You are likely to want to define $(PWD), and shorter names for
+top_srdir and abs_top_srcdir (we suggest $(src) and $(abs_src)).
+
 Global definitions
 ------------------