Size: Height and Width
Properties of the ScriptLine: BookFormat.
These 2 properties let you set the size of the QuarkXPress file that is your output file.
You usually do not need to set this property since, as soon as you have selected a Template, a message, such as this one, will be issued if this property needs to be set or changed, and clicking on that message will propose as option automatically setting the sizes to match the largest QuarkXPress file in the current script.
If you do set these properties manually, you will want to first select the type of size units you wish to use and then type in the size value, using the decimal separator used in your Windows settings (usually a period for the US and Canada, and a comma for the rest of the world).