Covers are items that can be installed on ducts to hide them, making them look like blocks.
A cover can be installed on any side of a duct by using it on the duct. It can be removed by using a wrench on it.
Installed covers do not affect how ducts work in any way. When a duct goes through a cover, a hole is made in the cover.
/td_blacklist_covercan be useful when configuring this blacklist; it returns the line to add to the list to disable a held cover.