File opening, :TRUNCATE

[Bernard S. Greenberg <BSG at SCRC-TENEX>]

Was it ever proposed or rejected that there be a :IF-EXISTS
:TRUNCATE, being like :OVERWRITE, except that the file content
is effectively set to empty before writing starts?  There is
need for such a thing, and it is a natural behavior on many
systems.  

The default :IF-EXISTS of :ERROR is not useful on file systems
that do not have versions (note that a version of :NEWEST
changes the default to :NEW-VERSION).   We propose that the
default :IF-EXISTS be changed to :SUPERSEDE for file sytems
that do not have versions.   

Is there any reason why :IF-EXISTS is ignored in :OUTPUT/:IO
instead of generating an error?