code: public int getSourceTree(Source source, SourceLocator locator, XPathContext xctxt)
            throws TransformerException
    {
  
      int n = getNode(source);
  
      if (DTM.NULL != n)
        return n;
  
      n = parseToNode(source, locator, xctxt);
  
      if (DTM.NULL != n)
        putDocumentInCache(n, source);
  
      return n;
    }
docs: Get the source tree from the input source.
  
  @param source The Source object that should identify the desired node.
  @param locator The location of the caller, for diagnostic purposes.
  
  @return non-null reference to a node.
  
  @throws TransformerException if the Source argument can't be resolved to
  a node.