Hi Gigot,
a good place to start reading about the googleon/googleoff tags is
http://code.google.com/apis/searchappliance/documentation/50/admin_crawl/Preparing.html#pagepart
However your question is not mentioned in that document. Nesting tags
in the way you are using them in your code example does not work. <!--
googleon: all--> voids all so far opened googleoff tags. So ".....some
code - Do we now return to the "googleoff: snippet" status? " will
probably appear in your search query snippets.
Best Regards
Mike