First stab T_REFREF docs

I am rather confident that this was added for some notion of symmetry
and completion. It's only half-implemented and there are no known users
in core or on CPAN. Candidate for deprecation (instead or in addition to
documentation?)?

diff --git a/ext/XS-Typemap/Typemap.xs b/ext/XS-Typemap/Typemap.xs
index 2aa4451..b74e9b0 100644 (file)
--- a/ext/XS-Typemap/Typemap.xs
+++ b/ext/XS-Typemap/Typemap.xs
@@ -694,7 +694,14 @@ NOT YET
 
 =item T_REFREF
 
-NOT YET
+Similar to T_PTRREF, except the pointer stored in the referenced scalar
+is dereferenced and copied to the output variable. This means that
+T_REFREF is to T_PTRREF as T_OPAQUE is to T_OPAQUEPTR. All clear?
+
+Only the INPUT part of this is implemented (Perl to XSUB) and there
+are no known users in core or on CPAN.
+
+=cut
 
 =item T_REFOBJ