Regular Expression nongreedy is greedy

A regular expression can only match a fragment of text that actually exists.

Because the substring 'ton' doesn't exist anywhere in your string, it can't be the result of a match. A match will only return a substring of the original string

EDIT: To be clear, if you were using the string below, with an extra 'n'

toooooooonoooooon

this regular expression (which doesn't specify 'o's)

t.*n

would match the following (as many characters as possible before an 'n')

toooooooonoooooon

but the regular expression

t.*?n

would only match the following (as few characters as possible before an 'n')

toooooooon

A regular expression es always eager to match.

Your expression says this:

A 't', followed by *as few as possible* 'o's, followed by a 'n'.

That means any o's necessary will be matched, because there is an 'n' at the end, which the expression is eager to reach. Matching all the o's is it's only possibility to succeed.

Regexps try to match everything in them. Because there are no less 'o's to match than every o in toooon to match the n, everything is matched. Also, because you are using o*? instead of o+? you are not requiring an o to be present.

Example, in Perl

$a = "toooooo";
$b = "toooooon";

if ($a =~ m/(to*?)/) {
        print $1,"\n";
}
if ($b =~ m/(to*?n)/) {
        print $1,"\n";
}

~>perl ex.pl
t
toooooon