$burning is a material shader parameter available in the and . It covers the
$basetexture with a
$burndetailtexture, to give the illusion that the model has been injured by fire. It does this by switching the clean version of the texture to a different .vmt with a "_burning" prefix, which slowly increases the opacity of the
$burndetailtexture up to 100%.
To do: Check for more games that have $burning.