When the output method is XML with indent="yes", the saxon:double-space attribute may
be used to generate an extra blank line before selected elements. The value is a whitespace-separated list of element names.
The attribute follows
the same conventions as cdata-section-elements: values specified in separate xsl:output
or xsl:result-document elements are cumulative, and if the value is supplied programmatically via an API,
or from the command line, then the element names are given in Clark notation, namely {uri}local.
The effect of the attribute is to cause an extra blank line to be output before the start tag of the specified elements.
