one of the documented procedures in this installation of the ACS
im_verify_form_variables   required_vars
What it does:
The intranet standard way to verify arguments. Takes a list of pairs where the first element of the pair is the variable name and the second element of the pair is the message to display when the variable isn't defined.
Defined in: /web/philip/tcl/intranet-defs.tcl

Source code:

    set err_str ""
    foreach pair $required_vars {
	if { [catch { 
	    upvar [lindex $pair 0] value
	    if { [empty_string_p [string trim $value]] } {
		append err_str "  <li> [lindex $pair 1]\n"
	} err_msg] } {
	    # This means the variable is not defined - the upvar failed
	    append err_str "  <li> [lindex $pair 1]\n"
    return $err_str