For those downloading these files from external modding sites rather than the Steam Workshop:
: A signature of many RED_LJ collections on the Steam Workshop is the implementation of physics for character hair, clothing, or anatomy.
: Drop the file into your game directory (e.g., \SteamLibrary\steamapps\common\Left 4 Dead 2\left4dead2\addons ).
If you are looking for details on this specific ZIP file for a blog post,