Texts in the humanities — as well as other texts — often exhibit, or their users wish to encode, multiple overlapping hierarchies using descriptive markup, e.g. by marking the physical phage features as well as textual and linguistic structures. The optional CONCUR feature of SGML has seldom been implemented and is not present in XML. Relying upon XPath expressions, the authors have implemented concurrent markup in standard XML. XSLT scripts are used to build and query across concurrent hierarchies. The authoring, validation, and procesisng of the document instances required for this technique use standard XML software.