Explain level prefixing

Change-Id: Ib2b422ee5ade99af4babbc1ab272cc32bb4ca413
diff --git a/script/korapxml2krill b/script/korapxml2krill
index 7d6f1e1..d01be37 100755
--- a/script/korapxml2krill
+++ b/script/korapxml2krill
@@ -1665,7 +1665,9 @@
 
 =item C<name>
 
-The key of the meta object
+The key of the meta object, that may be prefixed by C<corpus> or C<doc>, in case the
+C<E<lt>xenoDataE<gt>> information is located on these levels. The text level introduces
+no prefixes.
 
 =item C<project> (optional)