Re: Best way to use global params in templates to cove

In English, I need to cover in xsl all potential combinations of Customer
and Assembly (exists or not exists), for example:

1. If the Customer attribute does NOT exist in <link>, show the link {@url}
regardless of the param value for customer XYZ.
2. If the Customer attribute DOES exist, show the link ONLY if the attribute
matches the param value XYZ.
3. Also, various combinations of Customer AND Assembly attributes exist,
etc.

Seems like you want to use xsl:choose:
 <xsl:temlate match="link">
   <xsl:choose>
     <xsl:when test="not(@Customer)">
       <a href="{@url}> ... </a>
     </xsl:when>
     <xsl:when test="@Customer=$Customer">
       <a href="{@url}> ... </a>
     </xsl:when>
     <!-- add your various combinations -->?
   </xsl:choose>
  </xsl:template>

Only the first when clause whose test evaluates to true will
be executed, so be careful arranging them. Educate yourself
about xsl:otherwise too.