title: xsd:ID in Relax NG Schema
body: <p>I have the following xml file</p>
  
  <pre><code>&lt;bookshop&gt;
  &lt;book bid="1"&gt; Programming in C# &lt;/book&gt;
  &lt;book bid="2"&gt; programming in Java &lt;/book&gt;
  &lt;authors&gt;
   &lt;author bidref="1"&gt; person1 &lt;/author&gt;
   &lt;author bidref="2"&gt; person2 &lt;/author&gt;
   &lt;author bidref="1"&gt; person3 &lt;/author&gt;
  &lt;/authors&gt;
  &lt;/bookshop&gt;
  </code></pre>
  
  <p>then I made the following Relax NG schema </p>
  
  <pre><code>start=element bookshop{
  element book {attribute bid{xsd:ID},
                text}
  element authors{
      element author { attribute bidref{xsd:IDREF},
                           text}
                 }}
  </code></pre>
  
  <p>However, it always gives me error said that value of attribute bid is invalid must be an XML name without colons </p>