OK is used to label buttons in modal dialog boxes such as error messages or print dialogs, indicating that the user must press the button to accept the contents of the dialog box and continue. When a modal dialog box contains only one button, it is almost always labeled OK by convention and default, usually rendered to the screen in upper case without punctuation: OK, rather than O.K., Okay, or Ok. The OK button can probably be traced to user interface research done for the Apple Lisa.[62] The inspiration was likely the -ok parameter in Unix' find command.[63]