difference between xsl:param and xsl:variable

问题:

i am considering either one to use when defining an xsl:template name = myTemplate that will be called in another xsl file.

legacy code seems to use 'xsl:variable' when being used in xsl:template match="legacyTemplate"

so what's the difference between xsl:param and xsl:variable when using it in xsl:template name=myTemplate?

回答1:

The difference is that the value of an xsl:param could be set outside the context in which it is declared. For example, see:

<xsl:template ...>
   <xsl:param name="p" select="'x'" />
   <xsl:variable name="v" select="'y'" />
...

then you know that $v will always give you the string 'y'. But for $p the string 'x' is only a default: you will see a different value if the template is invoked with either xsl:apply-templates or xsl:call-template which contains an instruction such as:
<xsl:with-param name="p" select="'not x'" />

<xsl:param> may also be used outside xsl:template, at the top level in the stylesheet. The value of such a parameter may be set when the XSLT processor is called. How this is done depends on the processor and whether you call it from the command line or by program.