Naive question about binary encodings

["Linda Grimaldi" <grimlinda@earthlink.net>]

I'm sure this is really naïve of me, but I have to admit that I don't
understand why binary data cannot be sent within an xml document by
providing appropriately namespace-controlled attributes that identify an
element type as binary and specify its length.  For example:

<foo xml:mytype="binary" xml:binarylength="1776"> 
or some such thing, followed by 1776 octets of whatever one likes.  It's
kind of like MIME in some respects- as long as its type and length are
identified, you can do whatever you like with it.

It's so obvious that I am sure it has been rejected already, but, being
a mere implementor, I don't quite understand why.

Thanks,
Linda