<!DOCTYPE doc [
<!ELEMENT doc ((a | b)+, c) >
<!ELEMENT a EMPTY>
<!ELEMENT b EMPTY>
<!ELEMENT c EMPTY>
]>
<doc><a/><b/><c/></doc>
<!DOCTYPE doc [
<!ELEMENT doc ((a | b)+, c) >
<!ELEMENT a EMPTY>
<!ELEMENT b EMPTY>
<!ELEMENT c EMPTY>
]>
<doc><a/><b/><c/></doc>