code: private String getBaseURIOfIncludedStylesheet(StylesheetHandler handler, Source s)
              throws TransformerException {
          
  
          
          String baseURI;
          String idFromUriResolverSource;
          if (s != null && (idFromUriResolverSource = s.getSystemId()) != null) {
              // We have a Source obtained from a users's URIResolver,
              // and the system ID is set on it, so return that as the base URI
              baseURI = idFromUriResolverSource;
          } else {
              // The user did not provide a URIResolver, or it did not 
              // return a Source for the included stylesheet module, or
              // the Source has no system ID set, so we fall back to using
              // the system ID Resolver to take the href and base
              // to generate the baseURI of the included stylesheet.
              baseURI = SystemIDResolver.getAbsoluteURI(getHref(), handler
                      .getBaseIdentifier());
          }
  
          return baseURI;
      }
docs: Get the base URI of the included or imported stylesheet,
  if the user provided a URIResolver, then get the Source
  object for the stylsheet from it, and get the systemId
  from that Source object, otherwise try to recover by
  using the SysteIDResolver to figure out the base URI.
  @param handler The handler that processes the stylesheet as SAX events,
  and maintains state
  @param s The Source object from a URIResolver, for the included stylesheet module,
  so this will be null if there is no URIResolver set.