Current text width?

[Duncan Hothersall <dh@capdm.com>]

Hello all.

The following code (tested at contextgarden) illustrates my current problem:

--
\definetextbackground[TestBackground]
         [leftoffset=1em,rightoffset=1em,topoffset=8pt,
	bottomoffset=8pt,frame=on,location=paragraph]
\starttext
\starttextbackground[TestBackground]
Some text first, which behaves perfectly, and then a table:

\vbox{\bTABLE
\setupTABLE[column][1][width=0.3\textwidth]
\setupTABLE[column][2][width=0.7\textwidth]
\bTR\bTD I was hoping\eTD
\bTD that this table would make itself narrower according to the 
background offsets, like the text does. But it doesn't.\eTD\eTR
\eTABLE}
\stoptextbackground
\stoptext
--

The key is in the spec for column widths. I would like all the widths to 
be specified proportionally, but I need the right hook. I have tried 
\textwidth and \makeupwidth but neither seem to recognise the offsets 
introduced by the background. What I'd really like is a generalised 
solution, so that all tables just work no matter where they occur.

So - is there a parameter which represents the current width of the 
layout area, taking into account itemisations, textbackgrounds and 
anything else? Thanks.

[And thanks Hans for the earlier reference to details.pdf, which I am 
still trying to understand in order to allow my tables to extend into 
the margin. I'm working on it!]

Duncan
dh@capdm.com