7.1 Using DTDs in Documents

<!DOCTYPE root-element external-id [definitions]>

Introduced in the prolog after the XML declaration.
A DTD can be imported from an external file, specified inline, or a combination of the above

<?xml version="1.0" ?>
<!DOCTYPE live [
  <!ELEMENT live (eat | sleep)* >
  <!ELEMENT eat (#PCDATA) >
  <!ELEMENT sleep EMPTY >
  <!ATTLIST live
       xmlns CDATA #FIXED 'what:live' >
]>
<live xmlns="what:live">
  <eat>bread</eat>
  <eat>cake</eat>
  <sleep />
</live>

<?xml version="1.0" ?>
<!DOCTYPE live SYSTEM "live.dtd" >
<live xmlns="what:live">
  <eat>bread</eat>
  <eat>cake</eat>
  <sleep />
</live>

live.dtd:

<!ELEMENT live (eat | sleep)* >
<!ELEMENT eat (#PCDATA) >
<!ELEMENT sleep EMPTY >
<!ATTLIST live
xmlns CDATA #FIXED 'what:live' >

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