[This is preliminary documentation and subject to change.]
Properties are global variables used during an installation. All the properties are listed in the Property table of the installation database. Any property can be specified in the property table and will then be set at the launch of the installation. In addition, some properties are public and can be overridden at the command line or set dynamically during the installation using Standard actions or Custom actions. The names of public properties are always in all uppercase letters. Private property names are specified in the Property table and cannot be overridden because they describe the local system or operating system. For example, it is possible to author a package in which the public INSTALLLEVEL property is specified at the command line or chosen in a user interface. The WindowsFolder property however is set for the Windows platform. This property is specified in the Property table and cannot be overridden by an action or the command line. For more information on the individual properties see the Property Reference topic.