diff -r 1dd5633f5862 -r f7759beab4f2 README_REPOSITORY
--- a/README_REPOSITORY	Mon Oct 02 16:41:59 2017 +0200
+++ b/README_REPOSITORY	Mon Oct 02 16:42:12 2017 +0200
@@ -300,7 +300,9 @@
   ./bin/isabelle build -a -j2 -o threads=4  #test on multiple cores (example)
 
 See also the chapter on Isabelle sessions and build management in the
-"system" manual.
+"system" manual. The build option -S is particularly useful for quick
+tests of individual commits, e.g. for each step of a longer chain of
+changes, but the final push always requires a full test as above!
 
 Note that implicit dependencies on Isabelle components are specified
 via catalog files in $ISABELLE_HOME/Admin/components/ as part of the