Which are Java's system classes?

When reading some documentation about assertions, I found:

java -ea -dsa

"Enables assertions in general, but disables assertions in system classes."

Which are the system classes?

In which Package System class is defined?

System class belongs to the package java. standard output.

What are the members of System class?

Among the facilities provided by the System class are standard input, standard output, and error output streams; access to externally defined properties and environment variables; a means of loading files and libraries; and a utility method for quickly copying a portion of an array.

According to the assertions documentation, system classes are classes "which do not have an explicit class loader", i.e. the classes loaded by the bootstrap classloader. AFAIK that means the contents of rt.jar, the entire standard API.