Static functions to extract regular expressions from queries. The REs can
be used in caching stores that use the TWiki standard inline meta-data
representation to pre-filter topic lists for more efficient query matching.
for an example of usage.
Extract useful filter REs from the given query. The list returned is a list
of filter expressions that can be used with a cache search to refine the
list of topics. The full query should still be applied to topics that remain
after the filter match has been applied; this is purely an optimisation.