Added by berkley about 20 years ago
Added backtrack functionality. Backtracking works by passing a returndoc parameter. There can be more than one. If a document that is hit by a query is not of type returndoc then it searches the database for a related file of type returndoc. If one is found it is displayed, if no relation is found, the original is displayed.
Support was also added for an index of relations. the table xml_relation handles the all of the relation indexing.