I don't get where you think the term "obligation" applies. Based on "obligation" I think you could delete most if not all of the Inline::C documentation.

Rather than expecting the vague hints in Inline::C to lead to (a huge jump) ExtUtils/typemap then to perlguts then perlapi then "man strlen" to finally have the (C) '\0' character mentioned, I think it would be more than prudent for Inline::C to document this important and not obvious restriction and skip "typemap", "sv_setpv()", and "strlen()" and just say that a return value of type "char*" only works for strings terminated by "\0" (and not containing any non-terminal "\0" characters).

I also think an example of SV* and return newSVpvn( str, len ); deserves to be in the base manual, not burried in the "cookbook" (or the documentation of the restrictions on "char*" should point directly to an appropriate "cookbook" example). It would certainly be better than the example that uses SvPVX(), a macro that should mostly never be used.

But, of course, I don't find the author obligated to do much of anything.