[RS] - Soon to come: a packlet of routines for introspecting your Tcl/Tk interpreter. Here's just a starter... (note also the documentation format used with, but not requiring, [htext]).
 namespace eval inspect {}

set docu(inspect::value) {
This routine searches all global variables (scalar or array) for the specified value. Returns the list of variable names whose value matches. 
}
 proc inspect::value value {
    set res {}
    foreach i [info globals] {
        upvar #0 $i name 
        if [array exists name] {
            foreach j [array names name] {
               if [string equal $name($j)$value] {
                  lappend res ${i}($j)
               }
        } elseif [string equal $name $value] {
            lappend res $i
        }
    }
 }

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[LV] have you ever seen [tkinspect] - lots of neat features relating to [introspection]...

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See also the updated version of [tkinspect]: [TixInspect]
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[RS] admits he never looked at [tkinspect], and even less at [Tix] at all... and that the promise in the first sentence was never kept... but anyway, here's another little inspection tool that searches all defined procs for a given string:
 proc xref string {
    set res {}
    foreach proc [info procs] {
        if {[string first $string [info body $proc]]>=0} {lappend res $proc}
    }
    set res
 }

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[Arts and crafts of Tcl-Tk programming]