Concept
A scrollbar is an interaction technique or widget in which continuous text, pictures, or any other content can be scrolled in a predetermined direction (up, down, left, or right) on a computer display, window, or viewport so that all of the content can be viewed, even if only a fraction of the content can be seen on a device's screen at one time. It offers a solution to the problem of navigation to a known or unknown location within a two-dimensional information space. It was also known as a handle in the very first GUIs. They are present in a wide range of electronic devices including computers, graphing calculators, mobile phones, and portable media players. The user interacts with the scrollbar elements using some method of direct action, the scrollbar translates that action into scrolling commands, and the user receives feedback through a visual updating of both the scrollbar elements and the scrolled content. Although scrollbar designs differ throughout their history, they usually appear on one or two sides of the viewing area as long rectangular areas containing a bar (or thumb) that can be dragged along a trough (or track) to move the body of the document. This can be placed vertically, horizontally, or both in the window depending on which direction the content extends past its boundaries. Two arrows are often included on either end of the thumb or trough for more precise adjustments. The “thumb” has different names in different environments: on the Mac OS X 10.4 it is called a "scroller"; on the Java platform it is called "thumb" or "knob"; Microsoft's .NET documentation refers to it as "scroll box" or "scroll thumb"; in other environments it is called "elevator", "quint", "puck", "wiper" or "grip"; in certain environments where browsers use agnostic language to the scrollbar terminology, the thumb is referred to as the 'pea' for vertical movement of the bar and still use 'puck' for horizontal movement. Additional functions may be found, such as zooming in/out or various application-specific tools.
