title: Validation error while declaring attribute type as entity in XML
body: <p>Here is my DTD file.</p>
  
  <pre><code>?xml version="1.0" encoding="UTF-8"?&gt;
  &lt;!-- edited with XML Spy v3.0.7 NT (http://www.xmlspy.com) by Manukyan (YSU) --&gt;
  &lt;!ENTITY xxx "ccc"&gt;
  &lt;!ENTITY yyy "ddd"&gt;
  &lt;!ELEMENT book (author+, title, publisher)&gt;
  &lt;!ELEMENT author (#PCDATA)&gt;
  &lt;!ELEMENT title (#PCDATA)&gt;
  &lt;!ELEMENT publisher (#PCDATA)&gt;
  &lt;!ATTLIST title
      aaa ENTITY  #IMPLIED
  &gt;
  </code></pre>
  
  <p>And here is corresponding DSD file. </p>
  
  <pre><code>&lt;?xml version="1.0" encoding="UTF-8"?&gt;
  &lt;!DOCTYPE book SYSTEM "C:\Users\PC\Desktop\XML\XMLDB\XML\BOOK.DTD"&gt;
  &lt;book&gt;
      &lt;author&gt;asd&lt;/author&gt;
      &lt;title aaa="xxx"/&gt;
      &lt;publisher/&gt;
  &lt;/book&gt;
  </code></pre>
  
  <p>And I got a validation error saying that.
  Value part 'xxx' of attribute 'aaa' must be the name of unparsed entity.</p>