code: public void applyAttrSets(
            TransformerImpl transformer, StylesheetRoot stylesheet)
              throws TransformerException
    {
      applyAttrSets(transformer, stylesheet, m_attributeSetsNames);
    }
docs: Add the attributes from the named attribute sets to the attribute list.
  TODO: Error handling for: "It is an error if there are two attribute sets
  with the same expanded-name and with equal import precedence and that both
  contain the same attribute unless there is a definition of the attribute
  set with higher import precedence that also contains the attribute."
  
  @param transformer non-null reference to the the current transform-time state.
  @param stylesheet The owning root stylesheet
  
  @throws TransformerException