Apple codes used in Applescript-able applications

Question

I read some examples of code necessary to make an application Applescript-able, but I still don't understand if the Apple codes used to identify a command, a class, a property can be any value I want (with the exception of the code for the application class), and if they must be registered in some site.

Is there a list of codes with a particular meaning for Applescript?

Answer 1

This is what you want: AppleScript Terminology and Apple Event Codes. More can be found in this Apple document. Four-letter codes consisting solely of lower-case letters are reserved to Apple. Otherwise you're perfectly free to choose one.

You don't have to register them, as far as I know.

Answer 2

Choose your own. They must be unique. There is no way to know if they are unique, but they must be.

Love it.