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.