RPG Maker XP uses Ruby v1.8 as its scripting language. As your link explains, Ruby has a module called
Marshal that compresses Ruby objects into long strings of bytes. Official docs can explain it more in detail:
https://ruby-doc.org/3.2.2/Marshal.htmlHere's a very bare-bones example of what a marshaled object looks like:
class Test
def initialize
@name = 'foo'
@type = 'bar'
end
end
file = File.open('data_dump.txt', 'wb')
test_object = Test.new
Marshal.dump(test_object, file)
And then loading it back in is just a simple call of Marshal.load
test_object = Marshal.load(File.open('data_dump.txt'))
You just have to be cognizant of the order you dump and load things:
Marshal.dump(object_a, file)
Marshal.dump(object_b, file)
Marshal.dump(object_c, file)
# load in the same order as you dump...
object_a = Marshal.load(file)
object_b = Marshal.load(file)
object_c = Marshal.load(file)
As long as the class for the object you're dumping can be serialized to a string of bytes, you can call the Marshal functions on it. Otherwise, you're required defining the methods _dump and _load for the class (again, this is already explained in both articles).
I believe there are several parsers of marshaled data in various languages. If you really wanted to get your hands dirty and read byte code, you could write your own parser. On the Python side of things, there's this:
https://pypi.org/project/rubymarshal/I played with it for a while when I was exploring the idea of making an RMXP editor in Python.
This is a very high level overview of Ruby Marshal, but it's not a very easy thing to explain either. It took me a good few years of using Ruby before I understood the inner-workings of it. I don't think you're ready to handle this yet, especially without having any knowledge of RMXP (or Ruby for that matter).
With that said, since it seems like you're interested in Pokemon Essentials games, I can't help you with that. You're better off asking their forums (assuming people don't immediately frown upon the idea of editing save files over there).