in src/main/java/org/apache/commons/cli/DefaultParser.java [252:266]
private String getLongPrefix(final String token) {
final String t = Util.stripLeadingHyphens(token);
int i;
String opt = null;
for (i = t.length() - 2; i > 1; i--) {
final String prefix = t.substring(0, i);
if (options.hasLongOption(prefix)) {
opt = prefix;
break;
}
}
return opt;
}