Analisando o documento XML a seguir:

<?xml version="1.0"?>
<!DOCTYPE fibonacci [
<!ELEMENT fibonacci (fibonacci)*>
<!ELEMENT number (#PCDATA.)>
<!ATTLIST number index NMTOKEN #REQUIRED>
]>
<fibonacci>
<number>1</fibonacci>
<number index="1">1</number>
<number index="2">2</number>
<number index="3">3</number>
<number index="4">5</number>
<number index="5">8</number>
</fibonacci>

Podemos classificá-lo como: