[amibroker] pl clarify what stocknum == 0

[murthysuresh]

I am trying to understand the logic behind this watchlist cleanup 
routine. what is this symbol that has Status("stocknum") == 0

what guarantees that it will be true only for the first time during the 
exploration?
 

// clean up watchlists before starting
if( s = Status("stocknum") == 0 )
{
wlnumber = CategoryFind("wlUsualSuspectsLongFilter", 
categoryWatchlist ); 
List = CategoryGetSymbols (categoryWatchlist, wlnumber);
        for(i = 0; (Symbol = StrExtract(List, i)) != ""; i++)
                {
                        CategoryRemoveSymbol (Symbol, 
categoryWatchlist, wlnumber);
        }
}