Hope I understood you right.
Yep, it can. Look at the UFO-fort (in order to play it choose UFO from the Team Options and when creating the game in Game Schemes activate Fort Mode) or better say - at the Ray which the UFO uses to lift that car in the air. It's transparent and solid...Ok, not 100% transparent but you can still see the things behind it - rain animation and background. In order to 100% sure and if you don't want to wait for a more certain answer from the devs just open the image used for the UFO and edit the ray to be for example 90% transparent.

I see what you meant. That's wasn't my problem though ^^

What I meant was when I add a mask to a map, the map becomes not destructible. I shot the land, but everything remains clean. And only because I added a mask. I suppose.
(it's not about some option with the solid land, I check both states, nothing worked).
:/

Ah, now I understand and after rereading your first part. Well, in that case - wait for the devs.

Well I found something that could explain my problem.

Let's take the map "Basketball".

When you pick the basketball sheme, of course you can't destruct the land, because it is unchecked. But when you add your personnal sheme, with solid land checked... nothing changes. Weird? I guess the mask file must be for something in this. But I can't explain it.

In order to get an answer to your question faster, join the IRC channel. There is always someone from the dev-team there. btw When I'm ready with my exams and start working on the Manual again, I'm surely going to include the mask-thingie (if that's where the problem is) in the Tutorial-section on how to make themes, maps etc. If you get an answer not here but on the IRC channel, please post it here, so that I can include it. Thanks in advance!

Well, I've added a mask to my DigitalRope map.
First I filled the mask with red color.
The land is undestructable.
Then I filled with blue and the land became destructable but it seems the part of the mask was destroyed but the map didn't.

And white resolved the problem. But the the other problem is that the objects included to the map and not included to the mask aren't destroyed.

rbaleksandar > I will

pterodaktill > I made some other tests thanks to you. Unfortunately, I came with the same conclusions than you.

Everything described is precisely how the mask is intended to work.

it only has two colours, white and red.
Red indestructible, white destructible.

The reason parts of the mask that aren't given a colour are behind the hog, not destroyed, also deliberate. That's how the nets on the basketball map work.
Also useful for, say, background accents on a tunnel made in map using transparent.

Sooo, yeah. no bugs or anything. If you're using the unofficial mask thingy, that's exactly how it is intended to work.

Okay I see, thanks for your answer.