[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
        }
    }
 }

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

----
See also the updated version of [tkinspect]: [TixInspect]
----
[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
 }

----

[MJ] - Inspect an XML string using [Tk] and [tdom], call as `inspect::xml $xml`

  namespace eval inspect {
    proc xml {xml} {
      package require Tk
      package require tdom
      set doc [dom parse $xml]
      set tl [toplevel .$doc]
      wm protocol $tl WM_DELETE_WINDOW [namespace code [list cleanup $doc $tl]]
      ttk::panedwindow $tl.pane -orient horizontal
      ttk::treeview $tl.tv -selectmode browse -show tree
      bind $tl.tv <<TreeviewSelect>> [namespace code [list updateText $tl.txt %W]]
      text $tl.txt
      set struct [xmlStruct [$doc documentElement]]
      addChildren $tl.tv {} [list $struct]
      $tl.pane add $tl.tv -weight 1
      $tl.pane add $tl.txt -weight 2
      pack $tl.pane -expand 1 -fill both
    }

    proc cleanup {doc tl} {
      $doc delete
      destroy $tl
    }

    proc updateText {txt lv} {
      set node [lindex [$lv selection] 0]
      $txt delete 1.0 end
      $txt insert end [$node asXML]

    }


    proc addChildren {lv parent struct} {
      set index 0
      foreach element $struct {
        lassign $element name node children
        $lv insert $parent $index -id $node -text $name
        if {$children ne {}} {
          addChildren $lv $node $children
        }
        incr index
      }
    }

    proc xmlStruct {node} {
      set name [$node nodeName]
      if {$name eq "#text"} {
        return {}
      }
      set result [list $name $node]
      set nested {}
      foreach child [$node childNodes] {
        lappend nested [xmlStruct $child]
      }
      if {$nested ne {{}}} {
        lappend result $nested
      }
      return $result
    }
  }






[Arts and crafts of Tcl-Tk programming]