%E3%83%86%E3%83%BC%E3%83%96%E3%83%AB%E5%AE%9A%E7%BE%A9%E6%9B%B8%3Atag_name_sanitisation_rules.md

@@ -22,5 +22,6 @@ TagNameRule の after_update に TagName に対する置換処理を入れる．
 | 10 | `\*` | `_` | Time.current | Time.current | NULL |
 | 20 | `\?` | `_` | Time.current | Time.current | NULL |
 | 30 | `_+` | `_` | Time.current | Time.current | NULL |
-| 40 | `^_|_$` |  | Time.current | Time.current | NULL |
-| 50 | `^$` | `null` | Time.current | Time.current | NULL |
+| 40 | `_$` | `` | Time.current | Time.current | NULL |
+| 45 | `^(.+?\:)?_` | `\1` | Time.current | Time.current | NULL |
+| 50 | `^(.+?\:)?$` | `\1null` | Time.current | Time.current | NULL |