XEP-0377: Add the XML Schema

This has been tested with xmllint against every example in the XEP.

xep-0377.xml

@@ -26,6 +26,12 @@
   <supersededby/>
   <shortname>NOT_YET_ASSIGNED</shortname>
   &sam;
+  <revision>
+    <version>0.3.1</version>
+    <date>2023-04-03</date>
+    <initials>egp</initials>
+    <remark><p>Add XML Schema.</p></remark>
+  </revision>
   <revision>
     <version>0.3</version>
     <date>2021-06-21</date>
@@ -274,10 +280,67 @@
     </section2>
   </section1>
   <section1 topic='XML Schema' anchor='schema'>
-    <p>
-      An XML schema will be added before this specification moves to draft
-      status.
-    </p>
+    <code><![CDATA[
+<?xml version='1.0' encoding='UTF-8'?>
+
+<xs:schema
+    xmlns:xs='http://www.w3.org/2001/XMLSchema'
+    xmlns:sid='urn:xmpp:sid:0'
+    xmlns='urn:xmpp:reporting:1'
+    targetNamespace='urn:xmpp:reporting:1'
+    elementFormDefault='qualified'>
+
+  <xs:annotation>
+    <xs:documentation>
+      The protocol documented by this schema is defined in
+      XEP-0377: https://xmpp.org/extensions/xep-0377.html
+    </xs:documentation>
+  </xs:annotation>
+
+  <xs:import namespace='http://www.w3.org/XML/1998/namespace'
+      schemaLocation='https://www.w3.org/2009/01/xml.xsd'/>
+  <xs:import namespace='urn:xmpp:sid:0'
+      schemaLocation='xep-0359.xsd'/>
+
+  <xs:element name='container'>
+    <xs:complexType>
+      <xs:sequence>
+        <xs:element ref='report' minOccurs='0' maxOccurs='unbounded'/>
+      </xs:sequence>
+    </xs:complexType>
+  </xs:element>
+
+  <xs:element name='report'>
+    <xs:complexType>
+      <xs:sequence>
+        <xs:element ref='sid:stanza-id' minOccurs='0' maxOccurs='unbounded'/>
+        <xs:element ref='text' minOccurs='0' maxOccurs='unbounded'/>
+      </xs:sequence>
+      <xs:attribute name='reason' type='xs:string' use='required'/>
+    </xs:complexType>
+  </xs:element>
+
+  <xs:element name='spam' type='empty'/>
+
+  <xs:element name='abuse' type='empty'/>
+
+  <xs:element name='text'>
+    <xs:complexType>
+      <xs:simpleContent>
+        <xs:extension base='xs:string'>
+          <xs:attribute ref="xml:lang" use="optional"/>
+        </xs:extension>
+      </xs:simpleContent>
+    </xs:complexType>
+  </xs:element>
+
+  <xs:simpleType name='empty'>
+    <xs:restriction base='xs:string'>
+      <xs:enumeration value=''/>
+    </xs:restriction>
+  </xs:simpleType>
+
+</xs:schema>]]></code>
   </section1>
   <section1 topic='Acknowledgements' anchor='acknowledgements'>
     <p>