# of characters would be maximum number before splitting. mIRC will (and does now that it's included) cut lines at spaces whenever possible. Basically, if you set 400 characters and the 400th character was at the "x" in "maximum", it would split the line at the space before "maximum".
In any case, it works fine now, but I've disabled it because it was cutting stuff where I didn't want it to (not enough character) causing scripts I had that already split long lines to look wrong.
