Value is the install destination directory.
Value is the sources directory or subdirectory of Prefix.
Value is the executables directory or subdirectory of Prefix.
Value is library directory or subdirectory of Prefix.
Value is the project directory or subdirectory of Prefix.
Indicates that the project is to be installed or not. Case-insensitive value "false" means that the project is not to be installed, all other values mean that the project is to be installed.