Determines whether line numbering is enabled for documents loaded using this
DocumentBuilder.
By default, line numbering is disabled.
Line numbering is not available for all kinds of source: in particular, it is not available when loading from an existing XmlDocument.
The resulting line numbers are accessible to applications using the extension function saxon:line-number() applied to a node.
Line numbers are maintained only for element nodes; the line number returned for any other node will be that of the most recent element.