String arg=g.getOptarg();
int eqIndex=arg.indexOf('=');
if (eqIndex==-1) {
throw new IllegalArgumentException("the prefix declaration '"+arg+"' is not of the form PN=IRI.");
}
prefixes.declarePrefix(arg.substring(0,eqIndex),arg.substring(eqIndex+1));
}
break;
case kDefaultPrefix: {
String arg=g.getOptarg();
prefixes.declareDefaultPrefix(arg);