I do care. To quote from the OP.

What else should I be catering for? (Preferably with hints on how to detect and handle it :).

And from another post later in the thread:

Dealing with scalars that might be NVs, IVs, UVs and readonly is only the first part of the exercise. There are also RVs, tied scalars, blessed scalars etc. When I posted, I was hoping for insights into dealing with these also. I never expected to get hung up on dealing with readonly inputs.
I'm also curious if SvPVX() can yield you some pointers to interesting things, ...

I think I may be misunderstanding you? I look up SvPVX() and found 

#define SvPVX(sv)  ((XPV*)  SvANY(sv))->xpv_pv

[download]

And SvANY() is 

#define SvANY(sv)    (sv)->sv_any

[download]

Which doesn't clarify much?

Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.
Lingua non convalesco, consenesco et abolesco. -- Rule 1 has a caveat! -- Who broke the cabal?
"Science is about questioning the status quo. Questioning authority".
In the absence of evidence, opinion is indistinguishable from prejudice.

In reply to Re^8: XS/Inline::C concat *any* two SVs. (!all) by BrowserUk
in thread XS/Inline::C concat *any* two SVs. by BrowserUk

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