Question About r.location


In the challenge section it uses the following:

NSRange r = [n rangeOfString:@“AA” options:NSCaseInsensitiveSearch;

then, below that another line of code uses the “r” in the following way:

if (r.location != NSNotFound) [

I’m trying to understand how this works and can’t find in the book where this is described. If you could direct me where to look I would appreciate this.