questions about how to implement a gist index

Hi all,

I'm trying to contribute some improvements to the implementation of a gist
index that is part of an open source project and it would be really nice if
anyone could help me answer some questions.

I would like to use different data structures to represent the internal and
leaf entries. I think I have found several examples in the postgresql
source code where a variable length array is used to pack different data
consistently with the value of a "type" attribute. Is this the suggested
way to proceed, or would it be also possible to use two actually different
data structures? I at first considered this latter approach, but some
erroneous behavior suggested that maybe I am not fully clear about which
data structure should be produced or expected by some parts of the
implementation.

Could you please also help me understand the difference (if any) between
using the GIST_LEAF macro or the leafkey attribute of the GISTENTRY data
structure?

Thank you very much in advance,

Riccardo