diff --git a/preferred.conf b/preferred.conf
new file mode 100644
index 0000000..adcca5a
--- /dev/null
+++ b/preferred.conf
@@ -0,0 +1,14 @@
+# This file might contain simple rules that specify packages versions to be
+# installed. Allowed operators are '<', '>' and '='.
+#
+# For example, in order to force PHP to stay at version below 5.6:
+#
+# php<5.6
+#
+# MySQL server must be greater or equal than version 5.5:
+#
+# mysql-server>=5.5
+#
+# For a specific reason, cmake should stay at version 3.0.2:
+#
+# cmake=3.0.2