Figure 5-35 Scrolling by clicking in the gray area Pressing in the gray area causes the display of consecutive windowfuls of the document, until the user releases the mouse button, or until the location of the scroll box catches up to the location of the pointer. A windowful equals the height or width of the window, minus at least one unit of overlap to maintain the user's context. This unit of overlap is the same measurement determined for scroll arrow movement. By retaining this unit of information, you provide a reference point for the user.

On keyboards with function keys, the Page Up and Page Down keys also move the document view by a windowful.

Scrolling by Dragging the Scroll Box

The scroll box shows the position of the visible portion of the document in relationship to the whole document. If the scroll box is halfway between the top and bottom of the scroll bar, then what the user sees is about halfway through the document. To scroll the document, the user drags the scroll box. To see the beginning of the document, the user drags the scroll box to the top of the scroll bar; to see the end, the user drags the scroll box to the bottom. This behavior allows the user to quickly move around in the document. The user can get from one end of a long document to the other faster by dragging the scroll box than by clicking in the gray area or pressing the scroll arrows. Figure 5-36 shows how a user scrolls by using the scroll box.

Figure 5-36 Scrolling by dragging the scroll box

Figure 5-35 Scrolling by clicking in the gray area Pressing in the gray area causes the display of consecutive windowfuls of the document, until the user releases the mouse button, or until the location of the scroll box catches up to the location of the pointer. A windowful equals the height or width of the window, minus at least one unit of overlap to maintain the user's context. This unit of overlap is the same measurement determined for scroll arrow movement. By retaining this unit of information, you provide a reference point for the user.

On keyboards with function keys, the Page Up and Page Down keys also move the document view by a windowful.