--- trunk/lib/WebPAC/Normalize/Set.pm	2006/05/13 09:25:56	466
+++ trunk/lib/WebPAC/Normalize/Set.pm	2006/05/13 09:48:06	467
@@ -30,7 +30,15 @@
 =head1 SYNOPSIS
 
 This module uses C<conf/normalize/*.pl> files to perform normalisation
-from input records
+from input records using perl functions which are specialized for set
+processing.
+
+Sets are implemented as arrays, and normalisation file is valid perl, which
+means that you check it's validity before running WebPAC using
+C<perl -c normalize.pl>.
+
+Normalisation can generate multiple output normalized data. For now, supported output
+types (on the left side of definition) are: C<tag>, C<display> and C<search>.
 
 =head1 FUNCTIONS
 
@@ -50,11 +58,10 @@
 
 =head2 tag
 
-Define new tag for output
+Define new tag for I<search> and I<display>.
 
   tag('Title', rec('200','a') );
 
-By default, output will go into I<search> and I<display>.
 
 =cut
 
@@ -221,7 +228,7 @@
 
 sub prefix {
 	my $p = shift or die "prefix needs string as first argument";
-	return map { $p . $_ } @_;
+	return map { $p . $_ } grep { defined($_) } @_;
 }
 
 =head2 first