VQ vector value decode help

Hello,

I've been writing a decoder using the spec and it's unclear to me where 
the value [lookup_offset] comes from when performing VQ vector value 
decode (page 23 of the spec). The wording in the spec is very confusing 
to me. Someone asked this question before ( 
http://lists.xiph.org/pipermail/vorbis-dev/2002-September/015282.html ), 
but it went unanswered.

Could anyone help me (and anyone in the future) understand where this 
value is coming from?