one of the documented procedures in this installation of the ACS
my_export_url_vars   alist
What it does:
A little helper proc to be able to export a list (a very slight varient of a proc from utilities.tcl)
Defined in: /web/philip/tcl/prototype-defs.tcl

Source code:

    set params {} 
    foreach var $alist  { 
        if [eval uplevel {info exists $var}] { 
            upvar $var value 
            lappend params "$var=[ns_urlencode $value]" 
    return [join $params "&"]