Varlena Type Creation

Hi,

I'm working on a GiST opclass to support prefix searching as presented here:
http://pgsql.tapoueh.org/site/html/prefix/index.html
http://prefix.projects.postgresql.org/README.html
http://cvs.pgfoundry.org/cgi-bin/cvsweb.cgi/prefix/prefix/

In order to have a much more efficient index, I received the advice to
implement a prefix range datatype then base the picksplit() and union()
implementation on top of it.

So... where do I start to create a varlena datatype which has to store the 3
following values: text prefix, char start, char end.

It's not clear for me whether this is what I need to provide:

typedef struct
{
int32 vl_len_;
char start;
char end;
text prefix;
} prefix_range;

In particular, I've been taught a varlena definition can not contain pointers,
and I've no idea how to embed a text into another varlena...

Regards,
--
dim