Say I have an acme window with a $winid of 2.
If I type the following commands:

$ echo -n , | 9p write acme/2/addr
$ echo dot=addr | 9p write acme/2/ctl

I see the entire text of the window get selected.
I had assumed that if I then read addr that I would
get back two numbers, 0 and the final byte offset
of the file (it is a non-zero length file).

However, I get back two zeros:

$ 9p read acme/2/addr
          0           0

What am I missing?

Jim