The implementation of concurrent markup by Durusau and O'Donnell (Extreme Markup 2001) relies upon related but separate principles. First, markup, commonly described in tree notation, is actually metadata about PCDATA. Second, the membership of any "atom of PCDATA" ^[1] in a given hierarchy can be recorded as metadata for that PCDATA. These two principles have allowed the authoring and querying of overlapping hierarchies using standard XML software.

This presentation moves beyond the use of text snippets to illustrate overlapping hierarchies and applies the authors' technique to one of the classics of Western literature, John Milton's Paradise Lost. This research has resulted in the first release of overlapping texts for experimentation on overlapping hierarchies and in a firmer theoretical foundation for current and future research on this topic.