If the receiving device has holographic elements, it should implement the following:

1. Maintain a list of holo-blockers. This is a collection of keys that are preventing ("blocking") the holographic elements from being shown.
   
2. Check the list of holo-blockers in a timer and whenever the unit is powered on. Keys stay on this list while they are either:
   
   1. the OBJECT_ROOT of the unit (i.e., its chair), or
      
   2. in the attachment list of the unit.
      
3. When the list of holo-blockers is empty, the holographic elements can be shown again, and it is no longer necessary to periodically check the list. Remember to ensure that holographic elements are not visible while the unit is powered down.

The block-holo message should be sent by containers and equipment that tightly enclose the avatar, such as packing crates and power armor.

Sent by some devices over the light bus when they are installed. <device> is the device's one-word name, not its key. Implementation of this message is mandatory for batteries, but is not otherwise used.

Sent by some devices over the light bus when they are removed. <device> is the device's one-word name, not its key. Implementation of this message is mandatory for batteries, but is not otherwise used.

Any active device (see preamble at top of light bus article) may send this message to the HUD device to change its appearance on the HUD.

<uuid> should be the UUID of a texture icon to use, ideally a 32x32 pixel image or larger that has been designed to look good at 16x16 pixels, and consists of only white, transparent, and translucent white pixels.

Only works if using Native 8.6.3 and later. Builds before Oct 6, 2021 do not support this feature. Screen does not support this feature (see add-section instead.)

icon messages should generally be sent in response to the icon-q message, back to the key that sent the icon-q message. You can also determine the correct target for this message by sending devices to the controller.

Sent by HUD in later builds of 8.6.3 and newer to request that the recipient device send an icon message.

Something is connecting to the device that receives this message. Trigger connect effects.

Something is disconnecting from the device that receives this message. Trigger disconnect effects.

Send cable particles to <key>.

Sent by some devices over the light bus when they are re-installed. <device> is the device's one-word name, not its key. Implementation of this message is mandatory for batteries, but is not otherwise used.