A document needs to contain information (most of the time) about the layout of the document. So an HTML page is a document most of the time. The data is the TEX

A document needs to contain information (most of the time) about the layout of the document. So an HTML page is a document most of the time. The data is the TEXT and most of the HTML is there simply to tell the browser how to render the data. I think the argument above was that XML is great for creating document formats where as JSON or S-Expressions are great for sending data around.