Maybe it would help to point out that, with MUSH and all of the various flavors of codebase therein, there is a very distinct difference between what we refer to as:
Hardcode - this is the server codebase, the guts of the system, the parser and the database. This is what you get out of the box when you install a new game and start it up. There is one player object (GOD or #1) and one room. That's it. You get the help files and you're set to start building your little reality. This is what we refer to as 'under the hood', and there are generally three MUSH flavors: Penn, Rhost and MUX. All are designed differently, but once you are 'inside' a running game, they are about 90% similar. A person who knows Penn can operate on a MUX and vice versa, and just have to learn a few differences in commands. Coding (see below) is different from the standpoint of parameters and slight differences in behavior/output, but in general, a coder who knows MUX or Penn can code in Rhost, and vice versa.
Softcode- this is the part of building your little reality. If you have an RPG in mind, then you're going to need code to help players set their characters up. This is usually called CharGen (Character Generation). Here is where you build commands and rooms and help files that guide a player through putting together characters according to your game's rules. Next, you usually have code to support checking each other out. +FINGER is a very common example of this. On top of that, you get +WHO (which is slightly different than the stock WHO command), +WHERE and from here, a smattering of different commands that are designed to help players find other players for play.
Throw in here whatever your game needs. Want a command to allow players to summon others to their location? Very common. How about commands to alter your stats when you go from one werewolf form to another? Done. How about draining blood if you are a vampire? We have that in our games, too. Some games allow for invisibility, complete with snooping. Some games have commands for combat automation. Almost all games have health adjustment code that is run by the players themselves, staff or is automated in some fashion. Healing code? It's out there in MUSHes, too. Crafting on various levels? Yep, seen it, built em.
So understand that when you encounter a MUSH, you can almost always consider anything under 'help' as 'hardcoded'. Anything under '+help' is usually a softcoded system that someone has built in-game. It is stored on objects in a global Master Room so that those commands can be executed from anywhere on the game.
In general, the hardcode of MUSHes is rarely altered, hacked or touched, except in very fringe and custom cases. MUSHes differentiate themselves by softcode, by and large.