[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.