[xsl] select elements based on another element's attributes

["Lars Nyman" <larsnyman at 14designs dot com>]

Assume a widget element with some attr elements that defines some attributes
of a widget:

   <widget widget-id="402">
      <attrs>
         <attr name="p1" public="true"/>
         <attr name="p2" public="true"/>
         <attr name="p3" public="false"/>
         <attr name="p4" public="true"/>
      </attrs>
   </widget>

A widget-ref element may refer to the above widget element.  The widget-ref
specify values for some of the attributes of the widget using attributes
named according to the attr/@name of the widget.

   <widget-ref widget-id="402" p1="v1" p2="v2" p3="v3" p5="v5"/>


During processing, I would like to select all the attr elements of the
widget that have a "corresponding" attribute in the widget-ref element.
Alternatively, I would like to select all the attributes of the widget-ref
elements that have a "corresponding" attr element in the widget element.
With "corresponding" I mean that the widget-ref attribute name is equal to
the attr/@name, and as an additional constraint, the attr/@public must be
"true".
I intend to iterate over the attributes and emit name/value pairs.  For the
widget-ref element above I want to emit:
   p1=v1,p2=v2

Note:
   p3=v3 is not emitted because the "corresponding" attr element with
@name="p3" has @public="false"
   p5=v5 is not emitted because there is no "corresponding" attr element
with @name="p5"

So, I am looking for a select expression to use in place of either EXPR1 or
EXPR2 in the template below.

<xsl:template name="process-widget-ref">
   <xsl:param name="widget-ref"/>
   <xsl:param name="widget"/>

   <-- if iterating over widget-ref attributes -->
   <xsl:for-each select="EXPR1">
      <xsl:value-of select="name()"/>=<xsl:value-of select="."/>
      <xsl:if test="position()!=last()">,</xsl:if>
   </xsl:for-each>

   <-- if iterating over widget/attrs/attr elements -->
   <xsl:for-each select="EXPR2">
      <xsl:value-of select="@name"/>=<xsl:value-of
select="$widget-ref/@*[name()=name(current())]"/>
      <xsl:if test="position()!=last()">,</xsl:if>
   </xsl:for-each>
</xsl:template>


My initial attempt for EXPR2
   $widget/attrs/attr[@name=name($widget-ref/@*) and @public='true']
does not work since name($widget-ref/@*) returns the name of the first node
only.

Lars


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