Mods

@Jetspeed1001 cool!

@Nooneoone XML is kind of like HTML, though while HTML is the structure of websites, XML is kind of like a small database (i think. i'm not all that sure the difference between XML and a database)

@Nooneoone i know a bit of python, and i'm learning C#. i know html and css also

@Nooneoone yes, you can make a engine have 9000000 power, but cannot make new parts and stuff, etc (although you can change some stuff in the xml to get a really cool reflective color and i think transparent fuselage blocks. if that counts as a "texture")

@Jetspeed1001 ok :) i wanted to learn c# anyways (right now i only know python, javascript, and even though these arent languages html and css). So you are pretty much saying that XML is a way that i can for instance, make one of the engines be 9000000 power, but i can add anything new or any new textures etc.

XML is a way of storing information for the programming languages to use, it is not actually a programming language though, so you can't actually make mods using XML, however you can edit the properties of a part (size, rotation, etc) , XML modding is used a lot on SimplePlanes, and probably will be used a lot on SimpleRockets2 also, as it is a easy way to get past the designer's part customization limitations.
If you want to make mods for SR2 or SP you will need the Unity game engine, though i'm not yet sure what version is needed for SR2, but SP requires version 5.3.6f1. you can easily make custom maps to use in the game without knowing any programming at all. If you want to make stuff like weapons, new parts that do stuff, etc, you'll need to learn one of these programming languages: C#, Javascript, or Boo. Of course, there are many more programming languages but these are the ones that the Unity game engine uses.
I highly recommend C#, as most of the Unity community knows C#, and i'm 99% sure SP and SR2 is written in C#.
But that's just my opinion, it's your choice

@PrinceCaspian kk

@Nooneoone SP and SR2 are in unity and SR1 is in xml.

oh, i guess i mixed it up with another game? or is sp in xml?

It’s not done on XML. It’s done on unity.