text: :
  source file contains
  <pref:elName xmlns:
  Stylesheet has:
  <xsl:value-of
  rec says:
  9.2.4 fn:get-namespace-uri-for-prefix
  fn:get-namespace-uri-for-prefix( $element as element,
  $prefix as string) as string?
  Returns the namespace URI of one of the in-scope namespaces for $element,
  identified by its namespace prefix.
  saxon 7.4 says:
  Error at xsl:value-of on line 133 of file:/C:/sgml/files/xslt2/test1.xsl:
  An empty sequence is not allowed here
  I believe the first param to be an element,
  the second a string.
  Any clue why its an error please?
  TIA Dave: