[xslt] Redefining a variable

[ben <nicolas marsgui libertysurf fr>]

Hello,

I think I don't undertstand how the set of variables works with
stylesheets.

I have a stylesheet that defines a variable to a default value, and I
want to override the variable value with another stylesheet like this:

<xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
version='1.0'>
<xsl:import href="/the/main/stylesheet.xsl"/>
<xsl:variable name="my.var">the-value</xsl:variable>
</xsl:stylesheet>

When running xsltproc I've got the error message:

"runtime error: file /the/main/stylesheet.xsl line 172 element variable
Global variable my.var already defined"

Is-it only a warning, or do I do something wrong? With others processors
(XT, Xalan) there's no complaint.

Thanks,
BG