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