relaxng-driven editing

Hi,

if I understand it correctly, relaxng-based editors use validation algorithm as described
in the paper about Jing (based on derivatives) to offer first elements of the current
derivative as possible alternatives.

However, for many practical cases, the set of valid elements at any given point is determined
by a small context of the point; for docbook, for example, it is one parent and one preceding
element for all cases. 

RELAX NG in general may require a wider context for this approach; due to its context-dependence.
Is there a known algorithm to build distinct lookback contexts?

David Tolpin
http://davidashen.net/