Why cannot this be done by setting and returning an array of the attributes? The method you've currently described is really an abuse of upvar/uplevel, and should be avoided.
It creates the situation where procs are making assumptions about the callers variable space. Relying on procs to setup variables for you creates code that is difficult to maintain. Variables are used that pop up out of nowhere, with no indication who actually set them in the first place.
Upvar and Uplevel have been abused in this project, mainly, I think, to work around shortcomings of tcl that have since been improved/corrected in 8.x.
For proper use of Upvar and Uplevel, see Rob Mayoff's guidelines:
http://dqd.com/~mayoff/notes/tcl/upvar.html
