Gets a route handler that precedes this one (not necessarily immediately), may handle same request method, and matches on the same path or a prefix.
If the preceding handler’s path cannot be determined, it is assumed to match.
Note that this predicate is not complete: path globs such as
'*' are not currently
handled, and relative paths of subrouters are not modelled. In particular, if an outer
router installs a route handler
r1 on a path that matches the path of a route handler
r2 installed on a subrouter,
r1 will not be recognized as an ancestor of