DESCRIPTION
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-Adds a 'tag' reference in `.git/refs/tags/`
+
+Adds a 'tag' reference in `.git/refs/tags/`. The tag <name> must pass
+linkgit:git-check-ref-format[1] which basicly means that control characters,
+space, ~, ^, :, ?, *, [ and \ are prohibited.
Unless `-f` is given, the tag must not yet exist in
`.git/refs/tags/` directory.