How to gracefully check if a document exists relative

Hi there,

I'm transforming a XML document, and attempting to determine if a file
at a relative location exists.

The file as you would guess from the relative path exists one
directory up, and in another directory

Currently I'm using:

<xsl:choose>
            <xsl:when test="unparsed-text-available('../06_Regulations
Point in Time/125_2008_pit.xml')">
                <h1>Document found</h1>
            </xsl:when>
            <xsl:otherwise>
                <h1>Document NOT found</h1>
            </xsl:otherwise>
</xsl:choose>

However the unparsed-text-available only seems to check for the target
document relative to the location of the XSL file, not the XML.

I've also tried:
<xsl:choose>
        <xsl:variable name="common-uri"
select="resolve-uri('../06_Regulations Point in
Time/125_2008_pit.xml')" />
        <xsl:choose>
            <xsl:when test="unparsed-text-available($common-uri)">
           <h1>Document found</h1>
            </xsl:when>
            <xsl:otherwise>
                <h1>Document NOT found</h1>
            </xsl:otherwise>
</xsl:choose>

as well as:
<xsl:choose>
             <xsl:when
test="unparsed-text-available(document(''../06_Regulations Point in
Time/125_2008_pit.xml',/))">
             <h1>Document found</h1>
            </xsl:when>
            <xsl:otherwise>
                <h1>Document NOT found</h1>
            </xsl:otherwise>
</xsl:choose>


How would I go about gracefully checking to see if the document exists
relative to the document being transformed?  I see that the document
function has a way to enforce checking relative locations, but am
unsure how to put this all together.

Thanks for all your help.

Cal.