
A dead tree with a key. . .

. . .and a normal dead tree.
. . .or. . .

A pushable switch. . .

. . . and an unpushable one.
Since IDs are all about looks, images, shapes or whatever, does that mean we're shit outta luck?, well, ALMOST, here is what ID CAN
actually tell us.
The difference between:

A simply closed door. . .

. . . and a closed & LOCKED door.
Who gives a shit you might ask, well,
details like this ones are to be taken into account, for example, there are cases in which there is a locked door BEHIND another locked door, this is an obvious sign of the certain place to be
inaccesible or simply decorative, like the Kazordoon fortress example above, but there are certain places (specially places that we can now safely see with Xeno's spy (thanks @
DarkstaR)) that show an unlucked door behind a locked one which may be
ALSO decorative but gives us a
hint!
Except for a few exceptions; a key is mostly used for only
1 door, in which case, doors behind that closed door must need either
another key or to be open, if the bot shows us there's an
open door between a closed one (and taking into account that places with SEVERAL locked doors DO exist) we can only but conclude that THAT place is in fact; accesible, if not why would CIP bother differencing them?
What good is that? well, at least with this info we can know that certain particular places
ARE INFACT accesible, you will be sure you arent losing your time with something that's there JUST to look pretty, which is an abysmal difference when RPing.
But enough digressing, lets get to the real interesting stuff.
Thanks to IDs we can see the difference between:

Normal random chests. . .

. . . & quest chests.
So now that we think we can distinguish between accesible and non-accesible places, but we are not sure and everything else has failed, we can check if any container inside that locked place is in fact quest-giving or not.
Ofc there are exceptions to the rule, like the coffin in Draconia where key number 4 is hidden or this:

Which just contains a scarf but could aswell contain a key.
Let me use this pic as an example:

This is inside Hellgate, what concerns to the dead body, it has no volume so it most be quest related (Idk if this is a known quest).

Again, hellgate, those doors have the same ID, both are closed, but that's not all. . .

. . . all the containers on the first and second floor of that building
have volume, "
but wait! they may contain something anyway!" well. . . taking into consideration that the inside of that place
IS in fact locked by 2 different doors and it's structure doesnt have at least
1 quest container, I'd say it's simply a distraction, since the skeleton behind the quest door DOES NOT have volume and thus~ contains a quest-related item, so what does this tell me? Nothing concrete, really, but. . . it does help setting your priorities, something like: Forget about the house, focus on getting to the skeleton.