The String class is built-in to Flash. Just as there are many operations we can do with numbers, such as adding and subtracting, there are many operations we can do with Strings.
When you type s. the list of methods will appear.
You will see the letter D in the output window. Like most things in computers, numbering starts with 0. Thus, s.charAt(0) is the letter A.Strings in ActionScript, The String Class, String Functions, Anagrams, Cryptograms