Name a particular revision using <name>.
Tags are used to name particular revisions of the repository and are very useful to compare different
revisions, to go back to significant earlier versions or to mark branch points as releases, etc. Changing
an existing tag is normally disallowed; use -f/--force to override.
If no revision is given, the parent of the working directory is used.
To facilitate version control, distribution, and merging of tags, they are stored as a file named
".hgtags" which is managed similarly to other project files and can be hand-edited if necessary. This
also means that tagging creates a new commit. The file ".hg/localtags" is used for local tags (not shared
among repositories).
Tag commits are usually made at the head of a branch. If the parent of the working directory is not a
branch head, hgtag aborts; use -f/--force to force the tag commit to be based on a non-head changeset.
See hghelpdates for a list of formats valid for -d/--date.
Since tag names have priority over branch names during revision lookup, using an existing branch name as
a tag name is discouraged.
Returns 0 on success.