flash: how do i know how many times a string contains the substring?

for example, how do i know that the "hello world" string contains three letter l开发者_StackOverflow社区?

var hm:int = 0;
var index:int = 0;

while ((index = your_string.indexOf(your_substring, index)) != -1) {
    index++;
    hm++;
}

trace('how many: ' + hm);

Easy:

your_string.match( your_substring ).length;

Or cheesy:

your_string.split( your_substring ).length - 1;