Specifies the CLSID of a class that can emulate the current class.
HKEY_LOCAL_MACHINE\SOFTWARE\Classes\CLSID
\TreatAs = <CLSID>
Emulation is the ability of one application to open and edit an object of a different class, while retaining the original format of the object.
CoTreatAsClass, CoGetTreatAsClass, AutoTreatAs, IOleObject::EnumVerbs