The user may explicitly select an object, alter its properties (such as size or colour), or invoke other actions upon it (such as to move, copy, or re-align it).
The main focus of the interaction changes to become the users' data and other information objects that are typically represented graphically on the screen as icons or in windows.
For example, the earliest versions of the Smalltalk programming language had a command line interface that was nonetheless also clearly an OOUI,[6] though it subsequently became better known for its pioneering role in the development of GUIs, direct manipulation and visual metaphors.
At Apple, after using Pascal to implement six initial applications for Lisa, we discovered compelling reasons to change our programming language to incorporate more ideas from Smalltalk.
Lisa applications are now written in the language Clascal, an extension of Pascal featuring objects, classes, subclasses, and procedure invocation by message-passing.