Both of these attributes are designed to be
used as fragment identifiers.</p>
<p>In XML, fragment identifiers are of type <code>ID</code>, and
there can only be a single attribute of type <code>ID</code> per element.
Therefore, in XHTML 1.0 the <code>id</code>
attribute is defined to be of type <code>ID</code>. In order to
ensure that XHTML 1.0 documents are well-structured XML documents, XHTML 1.0
documents MUST use the <code>id</code> attribute when defining fragment
identifiers, even on elements that his