Some of the underlying XML syntax can be useful within documents. For example, comments can be included in the document, and will be ignored by the parser. Comments are entered using XML syntax. Other uses for XML syntax will be shown later.

XML sections begin with a <! tag and end with a >. These sections contain instructions for the parser rather than elements of the document. Everything between these tags is XML syntax. The DOCTYPE declaration shown earlier is an example of XML syntax included in the document.