Is it possible to define the paper size in troff? I've read
Kernighan's troff tutorial and `Typing Documents on the UNIX
System: Using the -ms and -mcs Macros with Troff' by Cherry and
Lesk, but it's not clear to me if there's a way to define a
different paper size.

For instance, I'd like to format a couple of things for A4
paper, which is most frequently used here in my neck of the
woods so-to-speak. From what I can tell, it's possible to change
margins, but I haven't seen any macros in ms(6) or registers
that would enable me to change the width and height of the page
itself.

Tips :)?

--Devon