No; these diagrams are not drawn from a semantic declaration language. They are drawn from ASCII diagrams. They are just inferring a "skin" made of nicer-looking Unicode symbols.
The examples don't show the source code next to them, but you can just view the page source in your browser (e.g. Ctrl-U in Firefox).
The examples don't show the source code next to them, but you can just view the page source in your browser (e.g. Ctrl-U in Firefox).