We should make the codes in #11581 to tutorials!

I second that. We should make #11581 into tutorials. I think it's a good idea.

I agree that presenting a program ready-to-use with simplices would be great. But I think the original request of @bangerth at #11581 (review) has not lost its validity: How do we deal with the code duplication, both in terms of teaching perspective and in terms of maintenance? I guess this would be an ideal case for some of these modern website content concepts, where all elements remain the same except for the 10 or 15 lines that actually need to be changed. I realize we are not having any such infrastructure yet, but I would strongly argue for reason about what options we have for combining the variants without giving the user two separate web pages with almost the same code, and with focus on the relevant changes.

@kronbichler Has a great idea. For sure it would be much more interesting to present step3 and the difference that arise when switching to simplices. A similar thing could eventually be to make a parallel version of step-6 and displaying the changes that arise. However, I am unsure how we could do this with the current web architecture. In all cases, I think it's better to temporarily have code duplication and strive for something better in the long term than to not show these features. In my opinion, features for which we do not have examples do not seem to exist in the eyes of most of our users and I understand them. Searching through Doxygen for a feature is a difficult endeavour.