> Are functions accessible via ruby/intern.h considered to be "public"
> API?     
> there without fear of the header file being removed?
>
> I'm using some of these functions, but I want to avoid a situation like
> we had with node.h.  

This topic is one of faq. summy of past discussion are

 - Ruby team never announced it's public APIs. and It was intended
"Intern"al functions.
 - However, many many gems depend on intern.h. so we can't break it
for compatiblity.
 - Some critical dangerous functions are gradually moving from
intern.h to internal.h.
   but it's not completed.
 - Further, intern.h might become just only have one line #include
<ruby.h> and almost functions move to ruby.h or internal.h in the
future. but it's still a status of just idea.

In short, It depend on your using functions. but almost functions are
ok at least 2.0. (2.0 has compatibility with 1.9). we have to accept
this historical accident. ;-)

Thanks.