more robust range on preceding comment-line;
no range for blank lines;
avoid recursive output_text/mark_range;
clarified Latex.output_token (no range) vs. Thy_Output.present_token (with range);
(*<*)
theory fakenat imports Main begin
(*>*)
text{*\noindent
The type \tydx{nat} of natural
numbers is predefined to have the constructors \cdx{0} and~\cdx{Suc}.
It behaves approximately as if it were declared like this:
*}
datatype nat = zero ("0") | Suc nat
(*<*)
end
(*>*)