You can use them as block comments.

But they are actually just reader macros which return nothing. They skip over the enclosed content.

Of course it does. #| this is commented out |#.

Comment syntax is usually something "special" in each language anyway.

And I didn't know it, hence me thinking there were 5 arguments.

That's all one expression, and there are 5 argument to the list procedure:

1.) a list containing three numbers, a symbol, and a character,

2.) a complex number,

3.) a string,

4.) the symbol "NIL",

5.) the empty vector.

I shouldnt have read it a second time on my phone. I was right the first time. :)