More clarification in guidelines wrt rule 17

next/guidelines.md

@@ -1200,9 +1200,27 @@ it will remove files that are not under `git(1)` control! Instead, see the
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 <p class="leftbar">
-Do **NOT** rely on these tools for any other rule, either.
+In other words, for `make clobber`, do something like:
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+
+``` <!---makefile-->
+    clobber:
+            ${RM} -f foo bar baz
+```
+
+and **NOT** something like this:
+
+``` <!---makefile-->
+    clobber:
+            -git clean -f
+```
+
+<p class="leftbar">
+And do **NOT** use `git` for any other tool either.
+</p>
+
+
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