ELEMENT: xsl:param
http://msdn2.microsoft.com/zh-cn/library/ms256096(VS.80).aspx
http://www.devguru.com/Technologies/xslt/quickref/xslt_element_param.html
We can think xsl:template is a function, the xsl:param is the parameter. It will provide more control to template.
ELEMENT: xsl:variable
http://www.devguru.com/Technologies/xslt/quickref/xslt_element_variable.html
http://msdn2.microsoft.com/zh-cn/library/ms256447(VS.80).aspx