proper context option: change of underlying Options.default will not survive PIDE "Prover.options" (e.g. change of Isabelle/jEdit plugin options);
(*<*)
theory fakenat imports Main begin
(*>*)
text\<open>\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:
\<close>
datatype nat = zero ("0") | Suc nat
(*<*)
end
(*>*)