Fix iso-authortitle sorting (patent holder and origyear) (rel. #99)

iso-authortitle.bbx

@@ -6,4 +6,37 @@
   sorting=nty,
 }
 
+% Sorting based on the default definition, but adding
+% holder and origyear to work with patent entry types.
+\DeclareSortingTemplate{nty}{
+  \sort{
+    \field{presort}
+  }
+  \sort[final]{
+    \field{sortkey}
+  }
+  \sort{
+    \field{sortname}
+    \field{holder}
+    \field{author}
+    \field{editor}
+    \field{translator}
+    \field{sorttitle}
+    \field{title}
+  }
+  \sort{
+    \field{sorttitle}
+    \field{title}
+  }
+  \sort{
+    \field{sortyear}
+    \field{origyear}
+    \field{year}
+  }
+  \sort{
+    \field{volume}
+    \literal{0}
+  }
+}
+
 \endinput