Of Swords and Parasols

So, I've been thinking about the whole "Gothic Shoujo Crack" thing some of these mangaka have going for them. Kaori Yuki, Higuri You, Matsuri Hino(though her brand and I just don't quite get along) and, I'm told, a number of Clamp things, though I've only seen it so far in Tsubasa starting in the Tokyo arc. (The first clue was the amnesiac princess, but once there were fraternal vampire twins with potententially interesting complexes there was just no going back.  It was Gothic Shoujo Crack masquerading as shounen action.)

Anyway, I know exactly what's in my head when I think of them, but it's not as easy for me to spell it out (as I tried to do to a little while ago.)  Off the top of my head, there's:

1.  The whole "strange, mysterious world" bit.  Even though most so far take place in a "normal" setting, present or past, the renditions make them seem completely different in the "huge, mysterious mansion" way.
2.  Darker supernatural elements.  (vampires, demons, fallen angels-in that world, that aren't of the demon variety-dark fae, etc.)
3.  Forbidden love in a messy way (vampires again, incest-fake and real-death, concerning age differences, living in other worlds, master/subordinate, etc.)
4.  Most I've read seem to involve some sort of epic quest/journey/world hopping for said love.  Mostly, the romance is OMG EPIC, even if one or both may do Non-Subtextual Important Staring And Declaring to another(but you never actually go "oh, triangle!" with them.)
5. ZOMG EVERY IMAGINABLE PAIRING IS ARGUABLY CANON WTF!
6.  Sometimes, you just have no idea what's going on, but the pretty and the angst didstract you from that.
7.  There's some sort of crazy crack in the form of a mad scientist or sadist or a machivellian sorcerer or some such.
8.  It makes my normal manga-reading standards completely disappear.
9.  Often, there's some sort of strange gender-bending involved.  (I mean, seriously...Sara/Setsuna/Kira:  Is that het romance with unrealized slash, or well-disguised femslash romance with unrealized het?  Half rhetorical.  No spoilers past vol 4, please, though I plan to catch up with what I have od Angel Sanctuary this week.)

Is there some sort of official definition or guide for the subgenre?  Anyone have other examples?  Because we all know that I have pitifully few titles to read, and always need more.

Spoiler code, in case anyone thinks they might need it:  <span style="color: #333333;background-color: #333333">Spoilers here.</span>