Create a new TraceText widget that is derived from the standard Text widget. Because it inherits all the
base options and methods it behaves just like a Text widget. Additionally, TraceText adds a
-textvariable option, which is a reference to a Perl scalar that defines the contents of the widget.
Based on the Tcl/Tk TracedText "overridden widget" by Kevin Kenny.
-textvariable
A scalar reference. The value of the variable defines the contents of the TraceText widget. Using
the keyboard to insert or delete text changes the value of the variable, and changing the variable
alters the contents of the TraceText widget.