It turns out that if you want to TextEdit to use more of the paper and shrink those ghastly 1 inch margins (which are, frankly, way too big for a lot of purposes) then you can’t do it. Well okay, you can do it by opening the RTF file in a real text editor and hacking the RTF directly. «\margl1440» sets the left margin to 1 inch (72 Adobe approved points in an inch, 20 thingummies in a point).
I don’t know what to be more appalled by. That this 1 inch margin is hard-coded into TextEdit (UTSL); that TextEdit ignores the Page Setup margins; that you have to edit the RTF by hand; that this works?
Can I also just say that if someone had said that the units specified in the RTF file were 127/7200000 of a metre then they would’ve been called insane.