.rul rul文件

The rul file is where the InstallScript custom actions are stored. It is a clear text file that the build engine compiles at build time. At least this is how it is used in a Basic MSI. I am not very versed in an InstallScript MSI

A .rul file is a text file containing InstallScript code (just as a .cpp file typically contains C++ code, and so forth). InstallScript projects typically have a source file with the special name setup.rul. For information about the InstallScript language, please see the InstallScript Language Reference section of the InstallShield help.

这个解释比较靠谱