From 65991900be98bfc929c75b196cc59b7e6675fb48 Mon Sep 17 00:00:00 2001
From: David Waltermire <david.waltermire@nist.gov>
Date: Fri, 10 Nov 2023 11:41:59 +0100
Subject: [PATCH] Added support for declaration of let expressions in
 constraints.

---
 schema/xml/metaschema.xsd | 21 +++++++++++++++++++++
 1 file changed, 21 insertions(+)

diff --git a/schema/xml/metaschema.xsd b/schema/xml/metaschema.xsd
index 7ccaecdd..83f09f3a 100644
--- a/schema/xml/metaschema.xsd
+++ b/schema/xml/metaschema.xsd
@@ -1044,8 +1044,27 @@
     </xs:complexContent>
   </xs:complexType>
 
+  <xs:complexType name="ConstraintLetType">
+    <xs:sequence>
+      <xs:group ref="ConstraintContentsGroup"/>
+    </xs:sequence>
+    <xs:attribute name="var" type="TokenDatatype" use="required"/>
+    <xs:attribute name="expression" type="MetaschemaPathType" use="required"/>
+  </xs:complexType>
+
+  <xs:group name="LetExpressionGroup">
+    <xs:sequence>
+      <xs:element name="let" type="ConstraintLetType" minOccurs="0" maxOccurs="unbounded">
+        <xs:annotation>
+          <xs:documentation>Declares a variable whose name is bound to the result of the Metapath expression. These variables can be used in target and other Metapath expressions used in constrains that are declared in the same context or in constraints declared in a child assembly, field, or flag.</xs:documentation>
+        </xs:annotation>
+      </xs:element>
+    </xs:sequence>
+  </xs:group>
+
   <xs:complexType name="DefineFlagConstraintsType">
     <xs:sequence>
+      <xs:group ref="LetExpressionGroup"/>
       <xs:choice maxOccurs="unbounded">
         <xs:element minOccurs="0" name="allowed-values" type="AllowedValuesType">
           <xs:annotation>
@@ -1119,6 +1138,7 @@
 
   <xs:complexType name="DefineFieldConstraintsType">
     <xs:sequence>
+      <xs:group ref="LetExpressionGroup"/>
       <xs:choice minOccurs="1" maxOccurs="unbounded">
         <xs:group ref="TargetedCommonConstraintsGroup"/>
       </xs:choice>
@@ -1128,6 +1148,7 @@
 
   <xs:complexType name="DefineAssemblyConstraintsType">
     <xs:sequence>
+      <xs:group ref="LetExpressionGroup"/>
       <xs:choice minOccurs="1" maxOccurs="unbounded">
         <xs:group ref="TargetedCommonConstraintsGroup"/>
         <xs:group ref="AssemblyConstraintsGroup"/>