[R] Basic graphics question

[Sean Davis]

I have a toy example given here:

    par(fig=c(0,1,0,0.05))
    par(mar=c(0,0,0,0))
    par(plt=c(0,1,0,1))
    par(oma=c(0,0,0,0))
    par(ann=F)
    plot(c(0,1),c(0,1),type='n',xlab='',ylab='',main='')
    rect(0,0,1,1,col='gray75')

What parameter am I missing to make the gray rectangle use the entire figure
region?  I am trying to build a plot from pieces, but there is a little bit
of margin left by the code above that prohibits the pieces from fitting
together perfectly.

Thanks,
Sean