[xsl] Seeking an elegant implementation of a graph traversal

["Costello, Roger L." <costello@xxxxxxxxx>]

Hi Folks,

I am seeking an elegant XSLT implementation for the following problem.

I have a Document consisting of a bunch of Sections. Each Section has a unique
identifier. Each Section may reference other Sections via an Include element,
e.g.,

<Document>
    <Section id="A">
        <Include idref="B" />
        <Include idref="C" />
    </Section>
    <Section id="B">
        <Include idref="D" />
    </Section>
    <Section id="C">
        <Include idref="D" />
    </Section>
    <Section id="D">
        <Include idref="A" />
    </Section>
    <Section id="E" />
</Document>

Problem: Write a function and pass a Section to it. The function outputs the
Section and all the Sections it Includes and all the Sections each of them
Includes, and so on.

Be sure there are no duplicates in the output.

Example: invoke the function with Section A. Here's the output:

A, B, C, D

Is there an elegant XSLT implementation of this graph traversal problem?

/Roger