Search String, can't find full stops (periods)


I’m trying to search a string for a full stop (period in American), but I can’t seem to get it to work properly:

This is a sample of my code:

var str:String = calc_content.text; //textbox content
trace(".")); //returns 0 whether it exists or not
trace("2")); //returns -1 if doesn't exist or the position (ie 2) if it does

Any help would be great!