Via the emphasis on descriptive markup, XML allows for elements of information/text to become self-aware, i.e. hold information on their own nature.
Information self-awareness has semantically structural and ontological aspects:
Who are you?
[structural semantic] I am a table cell in the second row, third column, of my parent table
[ontological semantic] I hold a maxim, from a given timespan in the classic age, in original and translated language versions.