In a graphical user interface on a computer monitor a toolbar is a panel on which onscreen buttons, icons, menus or other input or output elements are place. Earlier forms of toolbars were defined by the programmer and had set functions, and thus there was no difference between a toolbar with buttons or just a row of buttons. Most modern programs and operating systems however, allow the end user to modify and customize toolbars to fit their personal needs. Some prominent examples of customizable toolbars are panels of the GNOME and KDE desktop environments, functions of which range from expandable menus and buttons for applications, window lists, notification areas, clocks and resource monitors to volume controls and weather report widgets.