how can I do this the best way - xslt

Question

I have a variable in xslt that must contains several values which depends on the page.
I know that <xslt: variable> cannot do the job because variables cannot be changed.
Can xslt:param does the job and how can I change it value on the fly?
Roelof
Edit 1 : I try to explain what I want. I have a website which displays articles per month. What I really like is a script where I can filter the articles so only the articles of a particular month is displayed in pages. But I need to decide how many articles are displayed on each page. So the number of displayed articles is based on the month and the displayed page.

Answer 1

XSLT is a functional language, which, among other things, means that an xsl:variable or xsl:param, once specified cannot change its value.
This doesn't prevent the ability to express in XSLT the solution to any problem (XSLT is Turing-complete) and only requires one to change thinking based on the imperative programming paradigm.
Once you publish your specific problem, many readers will be able to provide complete XSLT solutions.
Here is a simple example:
We "accumulate" all wanted values in a variable, then output it:
<xsl:stylesheet version="1.0"
xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
<xsl:output omit-xml-declaration="yes" indent="yes"/>
<xsl:strip-space elements="*"/>
<xsl:variable name="vOddsAccumulator">
<xsl:apply-templates/>
</xsl:variable>
<xsl:template match="/">
<xsl:value-of select="$vOddsAccumulator"/>
</xsl:template>
<xsl:template match="*/*"/>
<xsl:template match="num[. mod 2 = 1]">
<xsl:value-of select="concat(., ' ')"/>
</xsl:template>
</xsl:stylesheet>
when this transformation is applied to the following XML document:
<nums>
<num>01</num>
<num>02</num>
<num>03</num>
<num>04</num>
<num>05</num>
<num>06</num>
<num>07</num>
<num>08</num>
<num>09</num>
<num>10</num>
</nums>
the wanted result is produced:
01 03 05 07 09