It happens in Objective-C:

    NSString *pattern = @"\\d", *string = @"੧";
    NSRegularExpression *regex = [NSRegularExpression regularExpressionWithPattern:pattern
                                                                           options:NSRegularExpressionCaseInsensitive
                                                                             error:nil];

    NSUInteger numMatches = [regex numberOfMatchesInString:string
                                                   options:0
                                                     range:NSMakeRange(0, [string length])];

    numMatches ? NSLog(@"%@ found by %@", string, pattern) : NSLog(@"%@ not found", string);

    // 2013-05-20 09:38:42.650 Regexperiment[17848:c07] ੧ found by \d