Usage of XSLT Params; <xsl:param> & <xsl:with-param>

Please explain me how best XSLT param can be used. in terms of <xsl:param> & <xsl:with-param>

<xsl:param> can be specified at the global level anywhere (as a child of xsl:stylesheet) or if it is within a template, it must be its child and it must precede any non-xsl:param child of xsl:template.

This is the facility that allows a template or the whole transformation (in case of a global xsl:param) to receive varying data from the caller/initiator of the template or of the whole transformation, respectively.

On the side of the caller/initiator of the template/transformation, parameters are passed by using an xsl:with-param instruction. it can be a child of xsl:apply-templates or xsl:call-template.

The name attribute of either xsl:param or xsl:with-param is mandatory. It identifies the parameter.

The select attribute of xsl:with-param may be used to specify any XPath expression, the result of whose evaluation is passed to the called/applied template.

Alternatively, the value can be specified in the content (body) of xsl:with-param.

xsl:with-param must have either a select attribute or a body. but not both of them.

An xsl:param can also have a select attribute or body. In this case, these specify the default value of the parameter and it is used if no parameter with this name has been specified by the caller.

Finally, here is a complete example illustrating most of these concepts:

<xsl:stylesheet version="1.0"
 xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
 <xsl:output omit-xml-declaration="yes" indent="yes"/>
 <xsl:strip-space elements="*"/>

 <xsl:param name="pTarget" select="'love'"/>
 <xsl:param name="pReplacement" select="'like'"/>

 <xsl:template match="/*">
  <xsl:call-template name="replace">
   <xsl:with-param name="pPattern" select="$pTarget"/>
   <xsl:with-param name="pRep" select="$pReplacement"/>
  </xsl:call-template>

  <xsl:text>&#xA;</xsl:text>

  <xsl:call-template name="replace"/>

  <xsl:text>&#xA;</xsl:text>

  <xsl:apply-templates select="text()">
   <xsl:with-param name="pPattern" select="$pTarget"/>
   <xsl:with-param name="pRep" select="'adore'"/>
  </xsl:apply-templates>
 </xsl:template>

 <xsl:template match="text()" name="replace">
   <xsl:param name="pText" select="."/>
   <xsl:param name="pPattern" select="'hate'"/>
   <xsl:param name="pRep" select="'disapprove'"/>

   <xsl:if test="string-length($pText) >0">
       <xsl:choose>
        <xsl:when test="not(contains($pText, $pPattern))">
          <xsl:value-of select="$pText"/>
        </xsl:when>
        <xsl:otherwise>
         <xsl:value-of select="substring-before($pText, $pPattern)"/>
         <xsl:value-of select="$pRep"/>

         <xsl:call-template name="replace">
           <xsl:with-param name="pPattern" select="$pPattern"/>
           <xsl:with-param name="pRep" select="$pRep"/>
           <xsl:with-param name="pText" select=
            "substring-after($pText, $pPattern)"/>
         </xsl:call-template>
        </xsl:otherwise>
       </xsl:choose>
   </xsl:if>
 </xsl:template>
</xsl:stylesheet>

When applied on this XML document...

<t>Sports stars we really love, love to hate, hate</t>

...the result is...

Sports stars we really like, like to hate, hate
Sports stars we really love, love to disapprove, disapprove
Sports stars we really adore, adore to hate, hate

Explanation:

1. The replace template is called twice. In both calls the pText parameter is omitted. Its default value is used by the called template.

2. The first call provides the pattern and replacement parameters, so "love" is replaced by "like".

3. Do note that the values of the global parameters $pTarget and $pReplacement are passed through. If the initiator of the transformation decides to pass other values (not the defaults that are used in this code) for these global parameters, these values will be passed to the replace template and not the defaults "love" and "like".

4. The second call doesn't provide any parameter values at all, so all defaults in the replace template are used -- the string "hate" is replaced by the string "disapprove".

5. Note that the replace template calls itself recursively, so that all occurrences of the pattern are replaced by the replacement.

6. Also, the values of the pText parameter of the recursive calls aren't static, but are dynamically calculated.

7. The third time the replace template is initiated from outside is via xsl:apply-templates. Here we also show that a template can have both a match and a name attribute at the same time and it is possible that such a template can be initiated both using xsl:apply-templates and xsl:call-template.

It's used to pass a param defined in another template:

<xsl:param name="globalParam"></xsl:param>

<xsl:call-template name="ABC">
  <xsl:with-param name="title" select="'A Title'" />
</xsl:call-template>

<xsl:template name="ABC">
  <xsl:param name="title"/>
  <xsl:value-of select="$title" />
  <xsl:value-of select="$globalParam" />
</xsl:template>