For example, it looks like Serial extends HardwareSerial, which extends Stream, which extends Print. But I don't think you can figure this out by reading the reference documentation on https://www.arduino.cc/ and it doesn't appear that you can easily navigate the class hierarchy in the Arduino IDE. They seem to go out of their way to hide the class hierarchy?
I guess I'm spoiled by modern languages that have automatically generated documentation, but it seems like there should be a more complete reference somewhere?