There's also [marking](/tags/marking), which is aliased to `markings` over on DB.
I suspect marking/markings was at some point used for body paints, non-standard coat markings and whatnot, but got misused for normal coat markings enough that it's now practically just an alternate tag for those.
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[@Fleur de Lis](/forums/meta/topics/tag-discussion?post_id=92013#post_92013)
I think `hoof heart` *was* that, originally, but got morphed into another variant of heart underhoof over time, similar to the above.
It's now the main tag for heart underhooves on DB, and `heart hoof`, `heart hooves` & `heart underhoof` are aliased to it...