> okay, so now we have an implementation by James and if you put that into a
> file called xcontentsJK.sty then you should be able to run the test file i
> appended below.
>
> my questions to this list would be now:
>
>  c) can you define the layout you are looking for?
>     if not:
>     - are there keys missing for the current templates?
>     - are there other templates missing that do radically different things?
>     - are the keys perhaps the wrong ones?

One more key : number-indent =l [0pt] \parindent
Perhaps it should be `first-line-indent'.  Used below.

For the contents I am trying to simulate I seem to need both
chapter and un-numbered-chapter instances. That would have implications
for the templates which write the table of contents file. (I also need
a demi-bold font, but thats by-the-by)
>
>  e) how difficult is it to implement a given design?

It's straightforward but fiddley,

here are my instances for the toc of Algebraic K-Therory (Springer, GTM
#147), The book only contains chapters, sections and `paragraphs'

\DeclareCollectionInstance{Ktheory}{contentsobject}{chapter}{JK}
    {pre-v-action = \DelayEvaluation{
                 \addpenalty{10000}\addvspace{0.5ex plus 1pt}},
     number-format = \textbf{\hfil Chapter~#1.\nobreakspace}, %Should be demi
     title-format  = \textbf{#1},                             %but this is bx
     pnum-format   = \textbf{\hfil#1},
     leaders-sep   = 100cm,
     object-indent = 2cm,
     number-indent = -2cm,
     number-width  = 2cm}

\DeclareCollectionInstance{Ktheory}{contentsobject}{unnumberchapter}{JK}
     {pre-v-action = \DelayEvaluation{
                      \addpenalty{10000}\addvspace{1ex plus 1pt}},
      title-format = \textbf{#1},
      pnum-format   = \textbf{\hfil#1},
      leaders-sep   = 100cm}

\DeclareCollectionInstance{Ktheory}{contentsobject}{section}{JK}
     {number-format = \hfil#1.\nobreakspace,
      leaders-sep   = 100cm,
      object-indent = 2cm,
      number-indent = -2cm,
      number-width  = 2cm}

\DeclareCollectionInstance{Ktheory}{contentsobject}{unnumbersection}{JK}
     {object-indent = 2cm+20pt,
      number-indent = -20pt,
      leaders-sep   = 100cm}

\DeclareCollectionInstance{Ktheory}{contentsobject}{paragraph}{JK}
     {leaders-sep   = 100cm,
      object-indent = 2cm,
      number-indent = -2cm,
      number-width  = 2cm}