Clean up: refactor event path calculation algorithm and retargeting algorithm

[hayatoito]

The event path calculation algorithm and retargeting algorithm should not have a strong dependency to events. In fact, these algorithms are being reused in elementFromPath, but it's confusing since events are not involved here.

Instead, these algorithms should be considered as more general algorithms, which are not related to events system. Define these in more general way, and make Events section (and other sections) should refer to it.