Require (allow) "xml:base"-attribute in XML Schema

Given a document such as the following:

<patch xmlns="http://example.com/ns/lxfs"
       xml:base="http:/example.com/publ/lxfs"
       id="http://example.com/lxfs/patches/3">

   <!-- ... -->
</patch>

How do I write an XML Schema to require (or even allow) the presence of the xml:base attribute with the fixed value of "http://example.com/publ/lxfs" on <patch>?

This is what I'd consider the "obvious" solution but xs:attribute[@name] is supposed to an NCName:

<?xml version="1.0" encoding="UTF-8"?>
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema"
           xmlns:lxfs="http://example.com/ns/lxfs"
           xmlns:xml="http://www.w3.org/XML/1998/namespace"
           targetNamespace="http://example.com/ns/lxfs">

  <xs:开发者_高级运维element name="patch" type="lxfs:Patch" />

  <xs:complexType name="Patch">    
    <xs:attribute name="id" type="xs:anyURI" use="required" />
    <xs:attribute name="xml:base" form="qualified" fixed="http://example.com/publ/lxfs" use="required" />
  </xs:complexType>
</xs:schema>

---

Change <xs:attribute name="xml:base"> to <xs:attribute ref="xml:base">, and add an xs:import for the schema for the XML namespace which can be found at http://www.w3.org/2001/03/xml.xsd. (Use a local copy rather than a reference to the one on the W3C

---

Just to clarify what Michael already posted, to get around this problem I first added this line to the top of my schema:

<xs:import namespace="http://www.w3.org/XML/1998/namespace"
           schemaLocation="http://www.w3.org/2001/03/xml.xsd" />

And then to attach this to an element, simply add the attribute:

<xs:attribute ref="xml:base" />

Wow, this saved me a lot of headaches.