Simon St.Laurent on XML Complexity. In this post to xml-dev Simon asserts that Post-Schema Validation Infoset (PSVI) which is required for the newer generation of XML related specs is building upon the wrong foundations.
I'm concluding from all of that that XML is not a good foundation for the kinds of information developers want from the PSVI, and that retrofitting XML to carry that information is perhaps the root cause of the complexity explosion we're seeing in W3C XML Schema and specifications which build on it. It seems to me that it might be wiser to use the PSVI directly for more abstract information modeling rather than expecting XML representations to carry the load.
XML works, sort of, but it seems pretty obvious that there are better approaches to representing information if you have all the information the PSVI provides rather than a simple "all is text" approach. This could easily be a binary format, though text might also be an option.
XML has done a wonderful job of convincing the world that it is possible to agree on base formats for some kinds of information, and that generic tools (parsers, editors, etc.) can be useful for a wide variety of specific problems. It seems reasonable to suggest that the lesson of XML is not "everyone must use angle brackets and text" but rather that "shared information formats are really useful when supported by a reasonable set of tools".