1. this is XPointer syntax: http://www.w3.org/TR/xptr-framework/#syntax
2. the TEI schemes defined in chapter 16 are meant to be well-behaved XPointer schemes
3. XPointer schemes may be chained, but may not be nested [everything depends on this assumption, so please attack or confirm]
4. In ch. 16, we have examples such as:
a. string-range(element(/1), 84,109)
with TEI-defined schemes containing W3C-defined schemes in (a), and TEI-defined schemes containing third-party-registered schemes in (b).