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