Separator attribute on xsl:for-each and xsl:apply-templates
If syntax extensions are enabled, then the xsl:for-each and xsl:apply-templates
         instructions allow a separator attribute, similar to the separator attribute on xsl:value-of.
The effect of the attribute is as follows. The attribute value template is expanded, once, using the outer context. The resulting string is converted to a text node. This text node is added to the result sequence after processing every item in the (sorted) input sequence, except the last.
For example, <xsl:apply-templates select="item" separator=", "/> inserts a comma and space into the output after
      processing every item element in the input sequence, except the last