Errors
Commands can return error messages as well as results. An error message is a message that is returned by an application, AppleScript, or the operating system if an error occurs during the handling of a command. The "Errors" section of a command definition, if present, lists errors that are likely to be returned by a particular command. This information can help you decide if you need to write error handlers to respond to the error messages that are returned. Error handlers are described in Chapter 8, "Handlers."Some "errors" are not the result of abnormal conditions but are the normal way you get information about what happened during command execution. For example, you use the Choose File command to ask the user to choose a file. When AppleScript executes this command, it displays a dialog box similar to the one you get when you choose Open from the File menu. If the user presses the Cancel button in the dialog box, AppleScript returns error number -128
and the error string"User canceled". Your script must handle this error
for script execution to continue.For a complete description of handling errors that occur during script execution, see Chapter 8, "Handlers."