On 2013–01–13 Malte Stien wrote:

> The trouble is that the page number is only a few millimetres wide
> and gets positioned on the inside edge of my outside margin.
> Hence, it does not end up close enough to the edge of the page. I
> guess, I would like to right-align it 4mm from the edge of a
> right-hand page and left-align it by the same amount from the edge
> of a left-hand page. Is that doable?

You can use the `command` key to hook in a custom macro which does
the placement.

\setuppagenumbering
  [alternative=doublesided,
   location={header, margin},
   style=bold,
   command=\PageNumberCommand]

\starttexdefinition PageNumberCommand #pageno
  \signalrightpage
  \doifrightpageelse
    {\rightaligned{#pageno}}
    {\leftaligned{#pageno}}
\stoptexdefinition


Marco