SPARQL support protege 5

Question

what's the level of support of SPARQL in protege 5.2.0 SPARQL Query Plugin 2.02?

I tried using

FILTER STRSTARTS(STR(?subject), STR(prefix:))

and I get

Unknown function 'http://www.w3.org/2005/xpath-functions#starts-with'

I can't seem to find a listing with the supported functions and capabilities.

Thanks