rr module has check_route_param(re) function that can be used to check
if local route header has a param that matches re. however, there does
not exist a function to find out what is the value of a given rr param.
for example, if route header has param ;param=foo, how to extract value
foo of param?
there is @rr.uri.params select that together with {param.value,name}
transformation might be able to do the job?
-- juha