When defining a secondary window, you can assign the ENTER key to activate a particular command button, called the default button, in the window. The system distinguishes the default button from other command buttons with a bold outline that appears around the button.
Define the default button to be the most likely action, such as a confirmation action or an action that applies transactions made in the secondary window. Avoid making a command button the default button if its action is irreversible or destructive. For example, in a text search and substitution window, do not use a Replace All button as the default button for the window.
You can change the default button as the user interacts with the window. For example, if the user navigates to a command button that is not the default button, the new button temporarily becomes the default. In such a case, the new default button takes on the default appearance, and the former default button loses the default appearance. Similarly, if the user moves the input focus to another control within the window that is not a command button, the original default button resumes being the default button.
The assignment of a default button is a common convention. However, when there is no appropriate button to designate as the default button or another control requires the ENTER key (for example, entering new lines in a multiline text control), you cannot define a default button for the window. In addition, when a particular control has the input focus and requires use of the ENTER key, you can temporarily have no button defined as the default. Then when the user moves the input focus out of the control, you can restore the default button.
Optionally, you can use double-clicking on single selection control, such as an option button or single selection list, as a shortcut technique to set or select the option and carry out the default button of the secondary window.