The messages you display in the virtual viewer are stored in a JAWS message file (.jsm) using the JAWS message format. You can format the text using spaces, carriage returns, tab stops etc. and JAWS retains the format of your message when it is displayed in the virtual viewer.
Unlike spoken messages, you cannot create and use long and short messages for use within the virtual viewer. If you want to account for different levels of verbosity, then you will have to speak the messages with your scripts instead of displaying them in the virtual viewer.
You can also use place holders in messages you display in the virtual viewer. The use of place holders allows for text to be added to the message at the time JAWS performs the script. For more information on creating messages and using place holders, see 8.0 Creating and Speaking Messages.