Layout and textwidth/textmargin

[nico <nicolas.marsgui@libertysurf.fr>]

Hello,

I wonder if it is possible to setup a layout with these requirements:

- it can be doublesided, that is, when doublesided the left margin (LM)  
and right margin (RM) are different and mirrored on right/left pages.

- the headings (section, etc.) start just after the left margin.

- the text body has an extra left text margin (TM) that is not mirrored.

Here is an example of the expected output in doublesided mode:

Left Page:
     LM      TM                          RM
|<--7--><-- 8-->                      <-5->|
|       1. This is a Title                 |
|                                          |
|               This is the text body      |
|               that has a bigger left     |
|               margin.                    |

Right Page:

    RM    TM                            LM
|<-5-><-- 8-->                      <--7-->|
|             The test continues on        |
|             This page.                   |
|                                          |
|     2. Another Title                     |
|                                          |

For singlesided documents I can play with a setup like this (the  
margindistances should be taken into account too):

\setuphead[section][margin=-TM]
\setuplayout[leftmargin=TM+LM,
              rightmargin=RM,
              backspace=TM+LM,
              width=\paperwidth-(RM+TM+LM)]

For doublesided documents I thought about using textwidth or textmargin,  
but in this case the text margin is applied on left and right (the text is  
in the middle).

Should I play with other setup parameters? What is the best way to achieve  
this?

Thanks for any hint,

Regards,
BG