mframed and alignment width

mframed and alignment width

[Hans-Joerg Schurr via ntg-context]

Hello everyone,

I'm using \startaligned with pairs and a distance to represent inference steps,
one per row.
Now I would like to sometimes add a vertical bar to the left of the rows and one
below the last row.  I was able to achieve this using \mframed, but now the
contented inside the framed box doesn't span the entire text width.

Here is an example:
\starttext

\startformula
\startalign[m=3, n=1,distance=2em plus 1 fil]
\NC 1 \NC 2 \NC 3 \NR
\NC 4 \NC 5 \NC 6 \NR
\stopalign
\stopformula

\startformula
\mframed[frame=off,bottomframe=on,leftframe=on]{
\startalign[m=3, n=1,distance=2em plus 1 fil]
\NC 1 \NC 2 \NC 3 \NR
\NC 4 \NC 5 \NC 6 \NR
\stopalign}
\stopformula

\stoptext

The second alignment should have the same width as the first one.  I played
around with the options of \mframed, but could not achieve this. :(

I will sneak in a a second small question: how can I adjust the distance between
the rows?

Thank you very much,
 Hans-Jörg
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