Fuseki configuration question

[Eric Scott]

I'm in the process of migrating a joseki configuration file to fuseki.  
I see this clause in example for <#service1>:

   fuseki:serviceReadWriteGraphStore "data" ;     # SPARQL Graph store 
protocol (Read and write)

It's not clear to me what this does.  What other values could one 
provide for this predicate, and what effect would those values have? 
Where is the value for this predicate referenced? I think the approprate 
reference for SPARQL Graph store protocol is 
<http://www.w3.org/TR/sparql11-http-rdf-update/>, but it's not giving me 
much of a clue.

Thanks,