I'm by know means an expert, but I'm incredibly proud of myself for having worked something out about this code. If you do:
div {
display: none;
}
a:hover > div {
display: block;
}
(Note the '>') You can contain the whole thing in an a tag, then, as long as your trigger (which can be in it's own div, or straight up in the a tag, or anything you want) is physically touching the revealed div, you can move your mouse from one to the other.
Maybe this isn't useful for a great deal, but I had to set my revealed div to overflow: auto, so sometimes it had scroll bars, which couldn't be used as soon as you move away from the div.
In fact, after finally working out how to make the revealed div, (although it is now a child of the trigger, not a sibling), sit behind the trigger, in terms of z-index, (with a little help from this page: How to get a parent element to appear above child) you don't even have to roll over the revealed div to scroll it, just stay hovering over the trigger and use your wheel, or whatever.
My revealed div covers most of the page, so this technique makes it a lot more permanent, rather than the screen flashing from one state to another with every move of the mouse. It's really intuitive actually, hence why I'm really quite proud of myself.
The only downside is that you can't put links within the whole thing, but you can use the whole thing as one big link.