Scrollbar

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Windows XP's vertical scrollbar

A scrollbar, or slider, is a graphical widget in a GUI with which continuous text, pictures or anything else can be scrolled, i.e., viewed even if it does not fit into the space in a computer display, window, or viewport.

Usually designed as a long rectangular area on one or two sides of the viewing area, containing a bar (or wiper) that can be dragged along a trough to move the body of the document as well as two arrows on either end for precise adjustments. The "wiper" has different names in different environments: on the Macintosh it is called a "thumb" 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". Additional functions may be found, such as zooming in/out or various application-specific tools. The wiper can also sometimes be adjusted by dragging its ends. In this case it would adjust both the position and the zooming of the document, where the size of the wiper represents the degree of zooming applied. A wiper that completely fills the trough represents viewing the entire document, at which point the scrollbar may temporarily become hidden.

Scrollbars can be seen as a computer representation of a thumb, with which you thumb through pages of documents.

[edit] Manipulation

While dragging the thumb is historically the traditional way of manipulating the widget, a scroll wheel may also be used. In addition, the arrow buttons may be clicked to scroll a small amount, or the trough above or below the thumb for a larger amount. Sometimes, both arrow buttons appear next to each other for quick, precise manipulation without having to drag the thumb or move the mouse great distances to the other arrow; one of them may also be duplicated so as to show at both ends of the bar, providing familiarity for those used to both separate and adjacent buttons.

Another system for manipulating them is to look at which mouse button was pressed. For instance, a left-click might cause it to scroll down, while a right click would scroll up, and the middle button could be used to place the thumb precisely. This form requires less fine motor skills, although it requires a multi-button mouse.

[edit] Customization

The ability and specific methods needed to customize the look and function of scrollbars can vary significantly based on which operating system or software application you are attempting to customize. The most commonly used method of altering the look-and-feel of the scrollbar in Web pages is to use a set of non-standardized CSS directives which at the time of this writing were only supported by Microsoft Internet Explorer versions 5.x or higher.