adding string-length values

Hi out there,

I'm currently trying to develop a stylesheet which does some special
transformation depending on the length of single elements and the accumulated
legth of all (prior) elements. The source XML documents looks something like
this:

<?xml version="1.0" encoding="UTF-8"?>
<Article>
	<Title>This is the title</Title>
	<Para>This is the first paragraph.</Para>
	<Para>This is the second paragraph.</Para>
	<Para>And this is the last parahraph.</Para>
</Article>


In my stylesheet I'd like to do something like this:

<xsl:variable name="mycounter" select="0"/>

<xsl:for-each select="//Para">
    <xsl:variable name="mycounter" select="$mycounter + string-length(.)"/>
    <p>Number Chars: <xsl:value-of select="$mycounter"/></p>
</xsl:for-each>


Unfortunately this does not result in what I want to do. XSL does not allow to
change the value of 'mycounter' thus giving me the length of each <Para>
element:

Number Chars: 28
Number Chars: 29
Number Chars: 31

instead of the accumulated length of all <Para> elements:

Number Chars: 28
Number Chars: 57
Number Chars: 89


I guess the solution for the problem is quite easy, but at the moment I do not
see how I could achieve the wanted result. So I hope that somebody can give me a
hint how to add up the length of certain elements (here: <Para>) !


Many thanks for any help in advance!

-  Zeljko


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