Here an XML Schema for the YAZ proxy configuration file. The schema, yazproxy.xsd is located in sub directory etc of the distribution.

<?xml version="1.0"?>
<!-- XML Schema for YAZ proxy config file.
-->
<xs:schema
  xmlns:xs="http://www.w3.org/2001/XMLSchema"
  xmlns:exp="http://explain.z3950.org/dtd/2.0/"
  xmlns="http://indexdata.dk/yazproxy/schema/0.9/"
  targetNamespace="http://indexdata.dk/yazproxy/schema/0.9/"
  >
 <xs:import namespace="http://explain.z3950.org/dtd/2.0/" 
      schemaLocation="zeerex-2.0.xsd"/>
 <xs:element name="proxy">
  <xs:complexType>
   <xs:sequence>
    <xs:element ref="target" minOccurs="0" maxOccurs="unbounded"/>
    <xs:element ref="max-clients" minOccurs="0"/>
    <xs:element ref="log" minOccurs="0"/>
    <xs:element ref="module" minOccurs="0"/>
   </xs:sequence>
  </xs:complexType>
 </xs:element>

 <xs:element name="target">
  <xs:complexType>
   <xs:sequence>
     <xs:element ref="url" minOccurs="0" maxOccurs="unbounded"/>
     <xs:element ref="target-timeout" minOccurs="0"/>
     <xs:element ref="client-timeout" minOccurs="0"/>
     <xs:element ref="max-sockets" minOccurs="0"/>
     <xs:element ref="keepalive" minOccurs="0"/>
     <xs:element ref="limit" minOccurs="0"/>
     <xs:element ref="attribute" minOccurs="0" maxOccurs="unbounded"/>
     <xs:element ref="syntax" minOccurs="0" maxOccurs="unbounded"/>
     <xs:element ref="preinit" minOccurs="0"/>
     <xs:element ref="exp:explain" minOccurs="0"/>
     <xs:element ref="cql2rpn" minOccurs="0"/>
     <xs:element ref="target-authentication" minOccurs="0"/>
     <xs:element ref="client-authentication" minOccurs="0"/>
     <xs:element ref="negotiation-charset" minOccurs="0"/>
     <xs:element ref="negotiation-lang" minOccurs="0"/>
   </xs:sequence>
   <xs:attribute name="default" type="xs:string" use="optional"/>
   <xs:attribute name="name" type="xs:string"/>
   <xs:attribute name="database" type="xs:string"/>
  </xs:complexType>
 </xs:element>

 <xs:element name="url" type="xs:string"/>
 <xs:element name="target-timeout" type="xs:integer"/>
 <xs:element name="client-timeout" type="xs:integer"/>
 <xs:element name="max-sockets" type="xs:integer"/>
 <xs:element name="bandwidth" type="xs:integer"/>
 <xs:element name="pdu" type="xs:integer"/>
 <xs:element name="retrieve" type="xs:integer"/>
 <xs:element name="preinit" type="xs:integer"/>
 <xs:element name="cql2rpn" type="xs:string"/>
 <xs:element name="target-authentication">
   <xs:complexType>
    <xs:simpleContent>
      <xs:extension base="xs:string">
        <xs:attribute name="type" type="xs:string"/>
      </xs:extension>
    </xs:simpleContent>
   </xs:complexType>
 </xs:element>

 <xs:element name="client-authentication">
   <xs:complexType>
    <xs:simpleContent>
      <xs:extension base="xs:string">
        <xs:attribute name="module" type="xs:string"/>
        <xs:attribute name="args" type="xs:string"/>
      </xs:extension>
    </xs:simpleContent>
   </xs:complexType>
 </xs:element>

 <xs:element name="negotiation-charset" type="xs:string"/>
 <xs:element name="negotiation-lang" type="xs:string"/>

 <xs:element name="keepalive">
  <xs:complexType>
   <xs:sequence>
    <xs:element ref="bandwidth" minOccurs="0"/>
    <xs:element ref="pdu" minOccurs="0"/>
   </xs:sequence>
  </xs:complexType>
 </xs:element>
 <xs:element name="limit">
  <xs:complexType>
   <xs:sequence>
    <xs:element ref="bandwidth" minOccurs="0"/>
    <xs:element ref="pdu" minOccurs="0"/>
    <xs:element ref="retrieve" minOccurs="0"/>
   </xs:sequence>
  </xs:complexType>
 </xs:element>
 
 <xs:element name="attribute">
  <xs:complexType>
   <xs:attribute name="type" type="xs:string"/>
   <xs:attribute name="value" type="xs:string"/>
   <xs:attribute name="error" type="xs:integer"/>
  </xs:complexType>
 </xs:element>

 <xs:element name="syntax">
  <xs:complexType>
   <xs:sequence>
    <xs:element ref="title" minOccurs="0"/>
    <xs:element ref="name" minOccurs="0" maxOccurs="unbounded"/>
   </xs:sequence>
   <xs:attribute name="error" type="xs:string" />
   <xs:attribute name="type" type="xs:string" />
   <xs:attribute name="marcxml" type="xs:string" />
   <xs:attribute name="identifier" type="xs:string" />
   <xs:attribute name="stylesheet" type="xs:string" />
   <xs:attribute name="backendtype" type="xs:string" />
   <xs:attribute name="backendcharset" type="xs:string" />
   <xs:attribute name="usemarconstage1" type="xs:string" />
   <xs:attribute name="usemarconstage2" type="xs:string" />
   <xs:attribute name="backendelementset" type="xs:string" />
  </xs:complexType>
 </xs:element>

 <xs:element name="title" type="xs:string"/>
 <xs:element name="name" type="xs:string"/>

 <xs:element name="max-clients" type="xs:integer"/>
 <xs:element name="log" type="xs:string"/>
 <xs:element name="module" type="xs:string"/>

</xs:schema>