Creatures Caves

Named variables are, aside of the size and perhaps speed disadvantages they might cause, not that awful. There is 3 levels of named variables:

NAME: These variables are just valid inside the agent that created them. They are basically like additional OV variables. You can use them when you actually should be running out of OVs (which I doubt will ever happen, there is 100 afterall) or when you want to store something in foreign agents without disturbing them in any way.
Creatures self would be an example. Let's say you have an agent which runs a complex check or something over creatures and then should mark them somehow. You could use an OV variable and hope no other script uses that particular one. Chances are good nothing will happen, but better safe than sorry.
Another thing is when you dynamically add or remove variables. I believe Moe's pathfinding for bees uses them. Remember room you are in and it's flower smell strength. Fly to another room. Is smell stronger than before? If no, turn back and try another direction, if yes add another NAME variable to remember this smell/roomID pair.
Once we reached our flowers and harvested nectar, go through your collected variables from the last to the first in order to find your hive again.
VAs or OVs are absolutely unqualified for this kind of code, so you go for NAME ones.

GAME: These are variables which are "known" within the entire world. You can use it e.g. for global rules that multiple agents can read and/or change. The breeding limits would be examples of such variables.
One unique thing about GAME variables is that you have to run an update command after changing them, so that scripts notice that it was changed. That command is RGAM. You can delay updating variables by not running RGAM, but it isn't the most reliable thing in the world. It is likely that some other agent RGAMs in the meantime because it has to update some other GAME variables.

EAME: The EAME variables are not very commonly used. The "E" stands for "Engine", i.e. they can be used across the entire game. Your current world, the world switcher, other worlds you load, all of them will know that EAME variable once you set it.
The ones already in the game influence options which are even "more global" than the breeding limit, such as if the hand actually shall be attached to the mouse or if the screensaver is allowed to activate while the game is running.

As Ghosthande mentioned, they take up quite a bit of space, so when you can be sure that you never ever need them again, you can destroy them (and that way completely free the memory they occupy) by using the commands DELN, DELG and DELE respectively.

For the syntax: you can use them pretty much like normal variables, but you always need to put the type it is (NAME, GAME, EAME) in front of it. Here an example:

* add a local variable
setv name "myvar1" 12

* get it's value, 12
outv name "mayvar1"

*do maths with it. Now it's 36
mulv name "myvar1" 3

* make a world-wide variable
setv game "spaces are supported too for names" 5

* does not exist yet, errors out
outv game "spaces are supported too for names"

* but now it does! we get a 5
rgam
outv game "spaces are supported too for names"

* make a variable that works across worlds
sets eame "SomeFunkyVariable" "named variables also support string values and agents"

* now we can even read our message in other worlds too
outs eame "SomeFunkyVariable"

* now let's remove all this stuff again
deln "mayvar1"
delg "spaces are supported too for names"
dele "SomeFunkyVariable"