'at' parameter in mtext(.., adj=0, outer=T) (PR#396)

"BDR" == Prof Brian D Ripley <ripley@stats.ox.ac.uk> writes:

    BDR> On Mon, 10 Jan 2000 john.maindonald@anu.edu.au wrote:

    >> Depending on the setting of par()$usr, the 'at' setting in mtext(..,
    >> adj=0, outer=T) may cause the text to appear in an anomalous
    >> position (e. g. in the first instance below, at the left of the plot
    >> region rather than at 'at=0' in the figure region), or the text may
    >> not appear at all.
    >> 
    >> If one does not set the 'at' parameter the text appears (with
    >> 'adj=0') on the far left of the plot region.  I assume this is also
    >> anomalous; at all events it is the behaviour that I wished to
    >> circumvent.

    BDR> I am afraid this is documentation confusion. There are no user
    BDR> coordinates in the outer margins, and at works like adj if
    BDR> outer=TRUE.  Indeed the example

    BDR> mtext(side=1,line=0.5,"Outer text",outer=T, adj=0)

    BDR> does work correctly for me: specifying adj=0 means put it at the
    BDR> extreme left, adj=1 at the extreme right, and adj=0 to centre it
    BDR> (on the display region, not the figure region).

    BDR> I will re-write the documentation.

Thank you!

Is there any reason why "at=" should be *valid* at all for mtext()?
I think this is the confusing part.
"at=" always makes (me) think of user coordinates,...