A common problem with toolkits is that their components are black boxes which can only be used as given. One either is happy with a standard window, having a standard title bar in the standard place, or one can write a new window procedure to assemble components as desired. There is rarely the option of passing the name of a different title procedure to the standard window. In ITS, the toolkit (style) programmer does not decide the specific view to be used for titles but inserts a TITLE environment into the window. The style expert can then change the view associated with the TITLE environment without reprogramming the window view.

Environments extend the power of style rules in creating consistency throughout an interface. Each object which has a title, such as a panel or dialog box creates that title by calling the view manager to insert an instance of the TITLE environment. The panel, or dialog box, doesn't know which view will be used to implement the title. A style rule which modifies the TITLE environment to choose a view which formats itself along with a date will cause each panel and dialog box to inherit the same, modified, title. The date it inserts in each title bar, likewise, will be consistently formatted since it is created by a DATE environment with the same view and other attributes.

Note that the same mechanism can be used to deliberately create inconsistencies. There is nothing to prevent...