Opacity/Placement

Many transparent blocks exhibit unique behavior when it comes to being placed or being placed on.

Placement on top of blocks
Everything can be placed on:
 * (top, closed)

Placement on the side of blocks
Everything can be placed on: Everything cannot be placed on:
 * (top, open)
 * (top, open)
 * (top, open)

Placement on bottom of blocks
Everything can be placed on: Everything cannot be placed on:
 * (the chorus flower will break)
 * (the chorus flower will break)
 * (the chorus flower will break)
 * (the chorus flower will break)
 * s
 * s

Doors and trapdoors
Doors and trapdoors behave in unique ways. The flat side of each block acts as an opaque surface, allowing anything to be placed on it. However, all other sides act as transparent blocks. Because of this, many blocks that can be placed on doors and trapdoors will not stay if the door or trapdoor is opened or closed.

Signs and banners can be placed anywhere on a door or a trapdoor and will never be destroyed unless the door or trapdoor itself is destroyed. Cakes and sea pickles can be placed on the tops of doors and trapdoors and will not be destroyed when the door or trapdoor opens and closes. Rails, redstone dust, redstone repeaters, and redstone comparators can only be placed on a closed trapdoor in the top half of a block, but will not be destroyed if the trapdoor is opened until the block is updated. All other blocks will be destroyed when the door or trapdoor changes states.

Shulker boxes
Shulker boxes typically act as a transparent block in that they allow everything to be placed on them. However, many of these blocks will be destroyed when the shulker box is opened. This behavior is also dependent on the rotation of the shulker box.

Upwards-facing shulker boxes
Upwards facing shulker boxes do not destroy most transparent blocks placed on their tops or bottoms when opened. However, some blocks stop the opening of the box.
 * (top only)
 * (top only)
 * (top only)
 * (top only)
 * (top only)
 * (top only)

While most blocks placed on top of upwards facing shulker boxes, the same is not true for blocks placed on the sides. Signs are not destroyed, but the following blocks are.

Sideways-facing shulker boxes
The following blocks stop a sideways shulker box from opening when placed on their front

Sideways facing shulker boxes destroy the following blocks when opened.
 * (top, side, and bottom only)
 * (top, side, and bottom only)
 * (side only)
 * (side only)
 * (side and bottom only)
 * (top, side, and bottom only)
 * (side only)
 * (top, side, and bottom only)
 * (side only)
 * (side only)

Downwards-facing shulker boxes
The following blocks stop downwards facing shulker boxes from opening.
 * (bottom only)
 * (bottom only)

Downwards facing shulker boxes do not destroy any blocks placed on their tops or bottoms when opened. However, they do destroy some when placed on the sides.

Pistons
All transparent blocks can be placed on unextended pistons. However, many blocks cannot be placed on extended pistons and/or are destroyed when pistons extend or retract.

Upwards-facing pistons
All blocks (except for vines) can be placed on the top or bottom of an extended upwards facing pistons. Only signs and banners can be placed on the sides of extended upwards facing pistons. However, they destroy most blocks when extending or retracting.

Sideways-facing pistons
The following blocks can be placed on extended sideways pistons.
 * (top, head, and back of piston only)
 * (head and back of piston only)
 * (head and back of piston only)
 * (head and back of piston only)
 * (head and back of piston only)
 * (head and back of piston only)
 * (head and back of piston only)
 * (head and back of piston only)
 * (head and back of piston only)
 * (head and back of piston only)
 * (head and back of piston only)
 * (head and back of piston only)
 * (head and back of piston only)

Downwards-facing pistons
All blocks (except vines) can be placed on the top and bottom of extended downward facing pistons. The only blocks that can be placed on the sides of extended downward facing pistons are signs.