a tag is stored under `$GIT_DIR/refs/tags` directory. git
imposes the following rules on how refs are named:
-. It could be named hierarchically (i.e. separated with slash
- `/`), but each of its component cannot begin with a dot `.`;
+. It can include slash `/` for hierarchical (directory)
+ grouping, but no slash-separated component can begin with a
+ dot `.`;
. It cannot have two consecutive dots `..` anywhere;