+ * | key | unmatched | prefix to node | return value |
+ * |--------------------|----------------|------------------|--------------|
+ * | a | not called | n/a | -1 |
+ * | logstore | not called | n/a | -1 |
+ * | logs | \0 | logs | as per fn |
+ * | logs/ | / | logs | as per fn |
+ * | logs/refs | /refs | logs | as per fn |
+ * | logs/refs/ | /refs/ | logs | as per fn |
+ * | logs/refs/b | /refs/b | logs | as per fn |
+ * | logs/refs/bisected | /refs/bisected | logs | as per fn |
+ * | logs/refs/bisect | \0 | logs/refs/bisect | as per fn |
+ * | logs/refs/bisect/ | / | logs/refs/bisect | as per fn |
+ * | logs/refs/bisect/a | /a | logs/refs/bisect | as per fn |
+ * | (If fn in the previous line returns -1, then fn is called once more:) |
+ * | logs/refs/bisect/a | /refs/bisect/a | logs | as per fn |
+ * |--------------------|----------------|------------------|--------------|