<!DOCTYPE my-root [
                      <!ELEMENT my-root  (a*)>
                      <!ELEMENT a  EMPTY>
                      <!ATTLIST a
                          val  CDATA "nothing"
                          fix   CDATA #FIXED "constant"
                          req  CDATA #REQUIRED
                          opt  CDATA #IMPLIED>
                  ] >
<my-root>
    <a val="something" fix="constant"
                       req="reading" opt="extra"/>
    <a req="no experience"/>
        <!-- OK: val = nothing, fix = constant,  opt absent. -->
    <a fix="variable"/>
         <!-- Invalid!  fix not constant and req unspecified. -->

</my-root>