Back in the day, one merely need look at
HKCR\.ext which would point to
HKCR is now a dynamic link to both
HKLM\software\classes, in a cascade pattern (local user first, then local machine).
However, now we also have this
..\explorer\FileExts registry tree, presumably at both user and machine levels as well. What does this additional complexity provide?
I don't know about you, but I am forever fighting Windows to correctly open my files, with Explorer hanging quite often, or failing to open a given file from explorer. And it seems quite arbitrary, where an install of say TextPad on one machine will appear to be 100% functional, whereas on another will result in only limited functionality with either Explorer or TextPad crashing when a file is attempted to be opened (say via the right click menu, or send-to, or drag & drop, or double click).
I've asked a few times and done myriad searches, and I have yet to find a comprehensive "this is what all keys related to file types are and do, and how Microsoft intends that they be used for coherent cooperation and proper function of a users system."