[incr Tcl] provides the extra language support needed to build large Tcl/Tk 
applications. It introduces the notion of objects, which act as building 
blocks for an application. Each object is a bag of data with a set of 
procedures or "methods" that are used to manipulate it. Objects are organized 
into "classes" with identical characteristics, and classes can inherit 
functionality from one another. This object-oriented paradigm adds another 
level of organization on top of the basic variable/procedure elements, and 
the resulting code is easier to understand and maintain.