+ hg init
+ hg add a
+ hg commit -m test -d 0 0
+ hg history
changeset:   0:acb14030fe0a
tag:         tip
user:        test
date:        Thu Jan  1 00:00:00 1970
summary:     test

+ hg tag -d 0 0 bleah
+ hg history
changeset:   1:863197ef0378
tag:         tip
user:        test
date:        Thu Jan  1 00:00:00 1970
summary:     Added tag bleah for changeset acb14030fe0a21b60322c440ad2d20cf7685a376

changeset:   0:acb14030fe0a
tag:         bleah
user:        test
date:        Thu Jan  1 00:00:00 1970
summary:     test

+ hg tag -d 0 0 bleah2
abort: working copy of .hgtags is changed!
(please commit .hgtags manually)
failed