From 38a026177df73a6a19028f7832c0741dfe1ab40c Mon Sep 17 00:00:00 2001
From: Nick Nicholas <opoudjis@gmail.com>
Date: Wed, 16 Dec 2020 23:38:49 +1100
Subject: [PATCH] add index/@to:
 https://github.com/metanorma/metanorma-bipm/issues/67

---
 grammars/basicdoc.rnc | 1 +
 grammars/basicdoc.rng | 3 +++
 2 files changed, 4 insertions(+)

diff --git a/grammars/basicdoc.rnc b/grammars/basicdoc.rnc
index b03b1e4..e567c59 100644
--- a/grammars/basicdoc.rnc
+++ b/grammars/basicdoc.rnc
@@ -226,6 +226,7 @@ hr = element hr { empty }
 pagebreak = element pagebreak { empty }
 
 index = element index {
+  attribute to { xsd:IDREF },
   element primary { PureTextElement+ },
   element secondary { PureTextElement+ }?,
   element tertiary { PureTextElement+ }?
diff --git a/grammars/basicdoc.rng b/grammars/basicdoc.rng
index dcb4c9a..07d2880 100644
--- a/grammars/basicdoc.rng
+++ b/grammars/basicdoc.rng
@@ -729,6 +729,9 @@
   </define>
   <define name="index">
     <element name="index">
+      <attribute name="to">
+        <data type="IDREF"/>
+      </attribute>
       <element name="primary">
         <oneOrMore>
           <ref name="PureTextElement"/>