diff --git a/bin/slubsipbuilder.pl b/bin/slubsipbuilder.pl
index a3ff39663c47de22ca260b107b04d330e66145da..9a5d94fce7f9a266f17d355fcc9c4adfff118d30 100755
--- a/bin/slubsipbuilder.pl
+++ b/bin/slubsipbuilder.pl
@@ -167,6 +167,7 @@ PATCH2
     return $result;
 }
 
+# specification SRU/SRW BSZ: https://wiki.k10plus.de/pages/viewpage.action?pageId=132874251
 sub get_mods_from ($$$$) { # $mods = ($url, $ppn, $searchkey, $recordschema)
     my $url = shift;
     my $ppn = shift; # example: "457035137"  for "Der Fichtelberg"