Using any of the keywords from the first two categories causes a compilation error when your script is first loaded. Using a reserved word from the third set can cause odd behavior problems if you attempt to use both your variable and the original entity of the same name in the same script. For example, the following script does not do quite what you think it should:In this case, you get an error saying that String is not an object. Many cases of using a pre-existing identifier aren't this obvious.var String; var text = new String("This is a string object");
Validator and Debugger!