Xeverous

@cppljevans I'm not sure what did you mean - I was only after compile-time decisions, such as which types are allowed by which parsers

> Yes, but my question was how are you proposing to do that. How - I'm not really sure, I haven't really gotten in the implementation of Spirit. > The...

Would such type ```cpp struct number { double value; number& operator=(double x) { value = x; return *this; } }; ``` work when inherited from `x3::position_tagged`?

In case of potential bugs - recently I have experienced enough bugs with Spirit that I better verify whether what I do is correct use of the library or not...

What do you think about adding static assert for 1-element fusions?

I mean placing a static assert that checks if a rule is instantiated using 1-element fusion. If so, make a compile error and mention to overload `operator=` instead.

Then I propose a tutorial page in the doc that will explain how to write a custom parser (some example boilerplate code and where to put what)

Assert straight at the beginning? Or "the beginning (function)" is already reused by recursion which causes problems in cases assert should not fire? Btw I think X3 should document some...

I actually don't remember who/where told me about inheriting from containers and `x3::variant`, but IIRC it was somewhere here on a different issue. All this stuff is an effect of...

The variant example is mentioned but: - (at least at the moment I was reading doc some time ago) - no mentions that 1-element fusion sequences are not supported -...