ToC depth (and headers) per section block

[Rik Kabel <context@rik.users.panix.com>]

How can I specify different section depths for different parts in a 
document in the TOC? That is, if the document structure is:

   Front Matter
   Body Matter
    Part 1
      Chapter 1
       Section 1
      Chapter 2
       Section 1
       Section 2
    Part 2
      Chapter 1
       Section 1
       Section 2
      Chapter 2
       Section 1
    Appendices
      Chapter 1
       Section 1
      Chapter 2
       Section 1
    Back Matter
      Notes
      Bibliography

How can I generate chapter and section entriess in the TOC for Part 1, 
but chapter entries only (no section entries) for Part 2 and the Appendices.

I currently do this by defining a new header equivalent to section and 
using that for Part 2 and Appendix sections. Since it is not included in 
the lists used by the contents combinedlist, it does not get set.

Is this the best way to do this?

If instead I want one depth for all body matter parts and a different 
depth for the appendices, is there a solution that could be keyed on 
system modes or on section blocks, thus moving all of the styling to the 
preamble (to use a LaTeX term)? I currently do that to support different 
header formats in the body matter and appendices, using the following 
method, but I suspect that there may be a more effective way to do that 
as well.

   \startsetups        [Header]
     \startallmodes    [print,*bodypart]
       {\color[PrintHeaderColor]{\PrintHeaderFont
{\llap{\getmarking[chapternumber]~}\getmarking[chapter]}}
     \stopallmodes
     \startallmodes    [print,*appendix]
       \color[PrintHeaderColor]{\PrintHeaderFont
         {\getmarking[chapter]}}
     \stopallmodes
   \stopsetups
   \setupheadertexts   []
   \setupheadertexts [\setups{Header}][][][\setups{Header}]

Again, I prefer a method that can be implemented in the preamble. (MKIV 
only.)

-- 
Rik Kabel
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