in C#, I use the following way to do transform, the I assign my extension
object to the xslArg, so in xsl, I can call functions in the extension
object. Now, I want functions in the extension object to call template in
the xsl, this way I can put some customized code into the template. I think
it is reasonable, but I don;t know how to do it, anyone has some idea on
this? Thanks.

xslt.Transform(xmlDoc, xslArg, textHTML, null);