Experimental XS APIs

In 5.18, when we added lexical subs, it was protected by a feature
that has an experimental warning.

I'm deeply attached to getting the signatures *syntax* into core, but
not attached at all to how its implemented.

Do we have anything right now at the XS level to explicitly opt in to
experimental APIs?

Say, add the functions, but put an

#ifdef EXPERIMENTAL_<function name>

#endif

So if anything outside of a bundled signatures module wanted to use
it, it would have to specifically set that #define

• Experimental XS APIs by Peter Martini
• Re: Experimental XS APIs by Zefram