C14n2 specifies a canonical XML document. This library writes 
such a document from an XML DOM as returned by the XML (or SGML) parser. 
The process takes two steps:
- Normalise the DOM
- Call xml_write/3 with 
appropriate flags
- [det]xml_write_canonical(+Stream, 
+DOM, +Options)
- Write an XML DOM using the canonical conventions as defined 
by C14n2. Namespace declarations in the canonical document depend on the 
original namespace declarations. For this reason the input document must 
be parsed (see load_structure/3) 
using the dialect xmlnsand the optionkeep_prefix(true).