What are PerlIO_sprintf and PerlIO_vsprintf for?

These functions are not called by anything in the Perl core, and 
cpan.grep.me

http://grep.cpan.me/?q=PerlIO_v%3Fsprintf

shows just 4 occurrences, none of which look like they result in actual 
calls.

• What are PerlIO_sprintf and PerlIO_vsprintf for? by Karl Williamson
• Re: What are PerlIO_sprintf and PerlIO_vsprintf for? by Nicholas Clark
• Re: What are PerlIO_sprintf and PerlIO_vsprintf for? by Karl Williamson
• Re: What are PerlIO_sprintf and PerlIO_vsprintf for? by Ricardo Signes
• Re: What are PerlIO_sprintf and PerlIO_vsprintf for? by Karl Williamson
• RE: What are PerlIO_sprintf and PerlIO_vsprintf for? by bulk 88