code: @Override
  	public void startPrefixMapping(String prefix, String uri) throws SAXException {
  		mNamespaces.addAttribute("", prefix, prefix.equals("") ? "xmlns" : "xmlns:" + prefix, "CDATA", uri);
  		if (!"".equals(uri)) {
  			try {
  				URI u = new URI(uri);
  				if (!u.isAbsolute()) {
  					System.err.println("*** (Canonical XML:) namespace URI " + u + " is not absolute");
  				}
  			} catch (URISyntaxException err) {
  				System.err.println("*** (Canonical XML:) namespace " + uri + " is not a valid URI");
  			}
  		}
  	}
docs: Receive notification of the start of a Namespace mapping.
  <p/>
  <p>By default, do nothing.  Application writers may override this
  method in a subclass to take specific actions at the start of
  each Namespace prefix scope (such as storing the prefix mapping).</p>
  
  @param prefix The Namespace prefix being declared.
  @param uri	The Namespace URI mapped to the prefix.
  @throws org.xml.sax.SAXException Any SAX exception, possibly
  wrapping another exception.
  @see org.xml.sax.ContentHandler#startPrefixMapping