How to pass parameter value to XSL?

Suppose I have a XSL as follows:

<xsl:stylesheet 
  xmlns:xsl="http://www.w3.org/1999/XSL/Transform" 
  version="1.0">
  <xsl:output method="html" encoding="utf-8" omit-xml-declaration="yes" indent="yes"/>
    <xsl:param name="sortKey" select="'firstname'"/>
</xsl:stylesheet>

Then a XML as follows

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<?xml-stylesheet type="text/xsl" href="XYZ.xsl"?>
<ABC>
     <firstname>GREG</firstname>
</ABC>

I want to pass a value to the XSL parameter firstname fro开发者_运维问答m XML. Can I do that? If yes, How?

It looks from the answers that this is not possible.

What about reading the value from the same XML and assigning it to the parameter. Can this be done? If yes, how?

Because the value you want as a parameter is in your base XML, you can simply enter a XPath expression for the paramater that specifies a default value.

<xsl:param name="sortKey" select="/ABC/firstname"/> 

Simply using an variable, would also be valid here, if the value was always going to be in the XML

<xsl:variable name="sortKey" select="/ABC/firstname"/> 

And then, to use this parameter/variable, you would simply do something like this

<xsl:template match="/">
    <xsl:value-of select="$sortKey" />
</xsl:template>

This would simply output the value GREG

Assuming that you're using .NET to do the transformation, the answer of this then duplicate question can be found here: Passing parameters to XSLT Stylesheet via .NET

The W3C has not proposed a mechanism. It's possible to define a new processing instruction which is capable of doing this. But if you're planning on using this in a browser or other existing tool, it's not a viable option to pass parameters into stylesheets which are invoked through processing instructions.

An alternative option is to place your "parameter" in an alternate document, and load it using something like the document() function.