So 
  <!DOCTYPE a [
    <!ELEMENT a (b, c)>
    <!ELEMENT b EMPTY>
    <!ELEMENT c EMPTY>
  ]>
  <a><![CDATA[  ]]><b/><c/></a>
would become:
  <!DOCTYPE a [
    <!ELEMENT a (b, c)>
    <!ATTLIST a xml:content-mode CDATA #FIXED "CDATA">
    <!ELEMENT b EMPTY>
    <!ELEMENT c EMPTY>
  ]>
  <a>  <b/><c/></a>
It's true that a non-validating parser will have difficulty with the latter
example, but that is solved by putting the xml:content-mode attribute on the
instance.