From Valve Developer Community
Revision as of 16:52, 21 September 2020 by Darnias (https://github.com/ValveSoftware/source-sdk-2013/blob/master/mp/src/game/server/baseentity.cpp#L4150 The input itself clears an attachment and doesn't set a new one)
Note:This template is deprecated. For new entity pages, please use Template:KV BaseEntity instead.
There are three extra bits you can add to this template:
vphystip(can't parent vphys objects)
triggerwarning(provide a dummy parent for map init)
cswarning(Counter-Strike: Source round restart oddness)