let me guess, zl union? or prepend/append? :) there is a third way, just cant recall it offhand now.

An object that starts with a number is a [pack] Try to open the Help.

I wouldn't do it this way. Not clear what it is and you cannot write [s 0 0] for example.

Another not-so-obvious thing about lists:

For some objects, they get distributed among inlets.

Except for an object that is just a number, which is an int/float. I am used to this behavior and was surprised that adding an argument changed it to a pack!

neat... didn't know that one either

As you probably know, int, float, and list are all (normally hidden) message selectors that are assumed whenever Max encounters a message that consists of (respectively) a single int, a single float, or a multi-item message that starts with a number. Similarly, typing a single int, a single float, or any multi-item list that starts with a number directly into an object box assumes an object of type int (or i), float (or f), or list (or pack). Viewed that way, it maybe makes more sense (although these shortcut conventions are not used that commonly in the tutorials or help files).

i usually use [list] — which also is nothing but a [pack] — because without a descriptive object name a [0 0 0 0] is not very good readable.

Using [list] instead of [pack] would make sense if there was also [unlist] instead of [unpack].

How about [unjoin] for your [unlist] ?