XML Parsers and Processors

Dear List,

For research issues I was looking for some papers, articles and tutorials about XML parsers and processors. They should not be on their use, but rather on the implementation issues, such as algorithms, data structures, context-free grammars and so on. Have already googled but did not find anything very relevant. Michael Kay already kindly sent me the link to his IBM developerworks on Saxon and it was very useful. Does anyone know something similiar for XML parsers?

Thanks in advance
Federico Meschini