Mysterious tag object property… can tags have parents?

So I was playing around with getting tag counts and decided to check out what properties the tag object / array actually has:

$tag[term_id] = 123
$tag[name] = xxx
$tag[slug] = xxx
$tag[term_group] = 0
$tag[term_taxonomy_id] = 123
$tag[taxonomy] = post_tag
$tag[description] =
$tag[parent] = 0
$tag[count] = 1

To my surprise, there’s a “parent” property. Now I’ve definitely read (by WP peeps no less) that there’s no hierarchy among tags (for whatever incomprehensible reason), but this seems to be suggesting the contrary. Do tags have parents in fact? Is this the property I would set? I.E. $tag[parent] =term_id?

Thanks for any help, it’d be great if this is actually possible.
– Lee