How to produce a record of changes made in an identity transform?

Hello all,
I had posted this query yesterday, but realised that the subject of the message 
didn't quite clarify my question, hence this repost. Apologies to those who 
have already seen this message.
Here's my problem:
I have the following stylesheet which essentially performs an identity 
transform on a given xml instance, producing a copy with
only slight changes (the e.g. below has one of these -- stripping out the 
concluding punctuation from element 'onlyNum' -- but the actual stylesheet will 
have more). I would like to produce another document that records these 
changes, at least as a list containing the original and changed node. this can 
be either text or xml, something on the lines of:
<onlyNum>E345.</onlyNum> changed to
<onlyNum>E345</onlyNum>
I have a feeling this could be done with xsl:result-document, but am not sure 
how to proceed. Any suggestions would be most welcome. 

Thanks in advance,

Munna

-----------
<xsl:stylesheet version="2.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform";>

<xsl:output method="xml" indent="no"
omit-xml-declaration="yes"/>

<xsl:template match="/|@*|node()">
<xsl:copy>
<xsl:apply-templates select="@*|node()"/>
</xsl:copy>
</xsl:template>

<xsl:template match="onlyNum">
        <onlyNum>
                <xsl:analyze-string select="."
regex="^(\w+)(\s)*([.])(\s)*$" flags="m">
                        <xsl:matching-substring>
                                <xsl:value-of select="regex-group(1)" />
                        </xsl:matching-substring>
                </xsl:analyze-string>
        </onlyNum>
</xsl:template>

</xsl:stylesheet>

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