-- Set more attributes in `make_client` (instead of doing it in `apply_rules`) and don't pass `XCB_NONE` as argument.
-- Internal nodes selectors/actions: labels?
-- Invisible state.
-- Restore built-in pointer grabbing?
-- `FILE *` instead of `char *` for writing the server response?
+- Add zoom feature (view point distinct from root).
- Use BSD `sys/{queue/tree}.h` for {list,tree} structures?