powertools score in solr.impex

Hello Friends,

I see for powertools the solrsoftfield as score. But I dont see any field with score. From where exactly this score value picked and solr sort will be done.

 # Define the sort fields
 INSERT_UPDATE SolrSortField;sort(indexedType(identifier),code)[unique=true];fieldName[unique=true];ascending[unique=true]
 ;$solrIndexedType:relevance;score;false