1.
Would it not be preferable to invert the choose as in

<xsl:for-each select="(  . . .)">
       <xsl:choose>
           <xsl:when test=". instance of xs:anyAtomicType">
               <xsl:value-of select="."/>
           </xsl:when>
           <xsl:otherwise>
               <xsl:apply-templates select="$foo,." />
           </xsl:otherwise>
       </xsl:choose>
   </xsl:for-each>

...
<xsl:choose>
 <xsl:when test=". instance of xs:integer"> ... </when>
 <xsl:when test=". instance of number()"> ... </when>
 <xsl:when test=". instance of xs:boolean"> ... </when>
 <xsl:when test=". castable as xs:integer"> ... </when>
 <xsl:when test=". castable as number()"> ... </when>
 <xsl:when test=". castable as xs:boolean"> ... </when>
 <xsl:when test=". castable as xs:string"> ... </when>
 <xsl:otherwise><xsl:apply-templates select="$foo,." /></xsl:otherwise>
</xsl:choose>

3.
What would be the best way to do this ?

4.
As for the use cases, aren't there more than might seem at first, especially where dynamic evaluation (ex: saxon:eval()) is used?

Cheers,
ac

a safer way is to use a global param, this prevents a static type error
(as the system can not know that you will not pass in a node) but if you
never do pass in a value then teh run time behaviour is as you wish:

<xsl:stylesheet version="2.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
<xsl:param name="foo" select="()"/>
<xsl:template name="x">
<xsl:for-each select="(1, 2, 3)">
        <xsl:choose>
            <xsl:when test=". instance of node()">
                <xsl:apply-templates select="$foo,." />
            </xsl:when>
            <xsl:otherwise>
                <xsl:value-of select="."/>
            </xsl:otherwise>
        </xsl:choose>
    </xsl:for-each>
</xsl:template>
</xsl:stylesheet>

$ saxon9 -it x stst.xsl
<?xml version="1.0" encoding="UTF-8"?>123

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