I just used the String # replace method with a regex:
var string:String = "BlaBlaBlaDDD12345";
var newString:String = string.replace(/[a-zA-Z]+/, "");
This will delete all words. If you are looking for more sophisticated regular expressions , I would mess with the Rubular regular expression tester online service .
:
var newString:String = string.replace(/[^\d]+/, "");
, , :
var newString:String = string.replace("BlaBlaBlaDDD", "");
() , , string.replace .