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Currently, we use JTidy to get "corrected" page source. This made of reading whole source, then tidying, then giving output XML to XML parser which will create tags. But good browser must show page before whole page will be loaded. Issue a thread, make some kind of "piped stream" (! this does not work as-is, see comments in TidyInputSource!) and renderer page while parsing. I am not sure Tidy can enhance pages progressively, you must evaluate.