ColumnHandler Shell Extension default details view

Looking for some Microsoft insight into this question...

I created a columnhandler shell extension.

I noticed that a few perceived types such as "audio" use a few registry
values to identify what coulmns to display in the default views (Detais,
TileInfo, InfoTip)

These values are located HKEY_CLASSES_ROOT\SystemFileAssociations\audio

These are my questions.

#1 How are the default columns chosen for a folder? (Does there have to be
more than one file of a type? Any other conditions?)

#2 If there are more than one type of file in a folder say MP3s, txt, xml,
video? Is the default details view used (Name, Size, Type, Name) or would
all the columns be merged?

#3 Is there a good source of documentation for this?


Thanks,
Shawn