Types of Widget
   In Tcl/Tk there are currently 15 types of widget. 
In alphabetical order they are
(see also see also library('tcltk/examples/widgets.tcl')):
     
button
     - a simple press button
     
 canvas
     - is a container for displaying "drawn" objects such as lines,
circles, and polygons.
     
 checkbutton
     - a button that hold a state of either on or off
     
 entry
     - a text entry field
     
 frame
     - a widget that is a container for other widgets
     
 label
     - a simple label
     
 listbox
     - a box containing a list of options
     
 menu
     - a widget for creating menu bars
     
 menubutton
     - a button, which when pressed offers a selection of choices
     
 message
     - a multi-line text display widget
     
 radiobutton
     - a button used to form groups of mutually interacting buttons
(When one button is pressed down, the others pop up.)
     
 scale
     - is like a slider on a music console. It consists of
a trough scale and a slider. Moving the slider to a position on the scale
sets the overall value of the widget to that value.
     
 scollbar
     - used to add scrollbars to windows or canvases. The scrollbar
has a slider, which when moved changes the value of the slider widget.
     
 text
     - a sophisticated multi-line text widget that can also display
other widgets such as buttons
     
 toplevel
     - for creating new standalone toplevel windows. (These windows are
containers for other widgets. They are not terminal windows.) 
 
   
Meet The Main Tk Widgets