--- a/src/sampleconf/fields
+++ b/src/sampleconf/fields
@@ -13,7 +13,7 @@
#####################################################
# This section defines what prefix the terms inside named fields will be
# indexed with (in addition to prefix-less indexing for general search)
-# ALL prefixes MUST be all UPPERCASE.
+# ALL prefixes MUST be all ASCII UPPERCASE (NO DIGITS)
#
# The field names should be the canonic ones, not the aliases defined in
# the following section. Don't change those which are predefined here,