Examples
1. Specify margins such that the default position used by .center is 50.
.leftmargin 10
.rightmargin 90
...
.center
.print 'This title is centered on column 50'
2. Move the right margin left by the number of characters specified by the value of the variable width.
.rm $width
3. Set the right margin to be the sum of the value of variable width and 3.
.rm $width+3
.noformfeeds