[xsl] Using node-set variables in predicates (another node comparison question)

["Chris Papademetrious christopher.papademetrious@xxxxxxxxxxxx" <xsl-list-service@xxxxxxxxxxxxxxxxxxxxxx>]

Hi everyone, and happy new year's!

Let's say I have a variable that contains a set of nodes:

<xsl:variable name="nodes" select="//(foo|bar|baz)"/>

In XPath 3.0, I can apply a template directly to this node-set variable (very
cool!):

<xsl:template match="$nodes">

However, what's the best way to use this node-set variable as a predicate
filter? For example, let's say I wanted to select every preceding sibling node
directly before each node in the variable:

<xsl:template match="preceding-sibling::node()[1][. intersect $nodes]">

The "interesect" operator works, but it's not intuitive. Is there a simple
Boolean operator that indicates whether a given node exists in a set of nodes?
([. = $nodes] compares text evaluations of the nodes, not the nodes
themselves.)

I hope the answer is not obvious, because I spent longer than I'd like to
admit trying to figure this out.  :)

- Chris