_MultiPicker.xsl

<xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform" xmlns:umb="urn:umbraco.library" version="1.0" exclude-result-prefixes="umb">
  <xsl:output method="xml" indent="yes" omit-xml-declaration="yes"/>
  <xsl:key name="document-by-id" match="*[@isDoc]" use="@id"/>
  <xsl:template match="MultiNodePicker" mode="multipicker">
    <!--
 Make possible to override the key used to retrieve nodes 
-->
    <xsl:param name="key" select="'document-by-id'"/>
    <!--

  	This does the equivalent of calling the key() function for every <nodeId>,
		collecting the resulting documents into a node-set.
		
		Ideally we could just apply templates to that set, but unfortunately the nodes
		will be processed in document order...
		
		So, would be cool to just be able to do this:
	
-->
    <!--  <xsl:apply-templates select="key($key, nodeId)" />  -->
    <!--
 Workaround for the above - still only accessing the lookup table once 
-->
    <xsl:variable name="nodes" select="key($key, nodeId)"/>
    <xsl:for-each select="nodeId">
      <!-- apply-templates, with mode=multipicker, so seperate templates can be used -->
      <!-- an example of this would be a product page, where related products are displayed in an aside -->
      <xsl:apply-templates select="$nodes[@id = current()]" mode="multipicker"/>
    </xsl:for-each>
  </xsl:template>
</xsl:stylesheet>

Cool - that's a neat idea, actually - at first I worried about potential endless loop (so would have suggested mode="Widget" or similar to distinguish from this) but that won't happen unless you create a DocumentType called MultiNodePicker :-)

BTW: There's a slightly improved (i.e. no for-each :-) version of the original here now: https://github.com/leekelleher/ucomponents-xslt/blob/master/uComponents.XsltTemplates/multipicker-helper.xslt

/Chriztian

Nice update! Interestingly if I remove my 'multipicker' mode from that apply-templates, it crashes IIS horribly, some sort of weird internal memory allocation issue. No stack trace, etc.

I'm making a note of that here, so I don't lose another 2 hours trying to debug it! :P