[XSLT2] Some common, generic grouping problems

Hello,

does anyone know of a comprehensive summary of ideas on how to tackle
many of the common grouping problems (URL, post, book)? When it comes to
grouping, I'm always lacking the smart ideas and concise code you
members of this list come up with.

For some of the grouping scenarios I managed to find generic solutions
(either on this list or in the spec itself), but for some I'm still at a
loss. I've collected a few examples below:

__Notes__

<arbitrary/> stands for one or many arbitrary elements in sequence. 
             There might be many different ones, even ones not known to 
             the transformation author in advance.

I'm thinking of grouping problems in terms of grouping likewise colored
nodes. Colors may have different brightnesses to give them special
meaning. I'm using the following:

dark-<color>    the first element in a group to be created
<color>         an element in a group to be created
light-<color>   the last element in a group to be created

<color>         a variety of colors identifying elements going into the 
                same group based in the same (basic) color.
                The color "none" or no color attribute at all specifies 
                an unknown color (e.g. because it never was explicitly set)



__Example XML #1__

<root>
    <arbitrary />
    <elem       color="dark-red" />
    <elem       color="red" />
    <arbitrary  color="none" />
    <elem       color="red" />
    <elem       color="light-red" />
    <arbitrary />
</root>

The task is to group all elements between pairs of 'dark-red' colored
and 'light-red' colored elements, i.e.:

<root>
    <arbitrary />
    <red>
        <elem       color="dark-red" />
        <elem       color="red" />
        <arbitrary  color="none" />
        <elem       color="red" />
        <elem       color="light-red" />
    </red>
    <arbitrary />
</root>



__Example XML #2__

<root>
    <arbitrary />
    <elem      color="dark-red" />
    <elem      color="red" />
    <arbitrary />
    <elem      color="red" />
    <arbitrary />
    <elem      color="dark-red" />
    <elem      color="red" />
    <arbitrary />
    <elem      color="red" />
    <arbitrary />
</root>

The task is to group all elements starting at 'dark-red' up to the last
red element before the subsequent 'dark-red' element, i.e.:

<root>
    <arbitrary />
    <red>
        <elem      color="dark-red" />
        <elem      color="red" />
        <arbitrary />
        <elem      color="red" />
    </red>
    <arbitrary />
    <red>
        <elem      color="dark-red" />
        <elem      color="red" />
        <arbitrary />
        <elem      color="red" />
    </red>
    <arbitrary />
</root>



__Example XML #3__

<root>
    <arbitrary />
    <elem      color="red" />
    <elem      color="red" />
    <elem      color="dark-red" />
    <elem      color="red" />
    <arbitrary />
    <elem      color="red" />
    <elem      color="dark-red" />
    <arbitrary />
</root>

The task is to group by adjacent color, but force starting a new group
when the color is dark, i.e.:

<root>
    <arbitrary />
    <red>
        <elem      color="red" />
        <elem      color="red" />
    </red>
    <red>
        <elem      color="dark-red" />
        <elem      color="red" />
    </red>
    <arbitrary />
    <red>
        <elem      color="red" />
    </red>
    <red>
        <elem      color="dark-red" />
    </red>
    <arbitrary />
</root>


I guess one of the main difficulties I'm struggling with currently are
the <arbitrary /> elements. Should I try to "color" them before starting
the grouping? How would this best be done in example #2? Or is trying to
add the "missing" colors the wrong approach?

-Christian